Adding support for FS OS

[PaperbagLife]

The goal of this PR is to help merge #3372, since the original poster did not respond to the comments.
I did not write the code, I only added tests.
FS OS would be helpful to have.

output from show test:

============================================================================ test session starts ============================================================================
platform linux -- Python 3.10.16, pytest-8.3.5, pluggy-1.5.0 -- /usr/bin/python3.10
cachedir: .pytest_cache
rootdir: /home/ticktock/netmiko
configfile: setup.cfg
collected 25 items                                                                                                                                                          

test_netmiko_show.py::test_failed_key SKIPPED (Not using SSH-keys)                                                                                                    [  4%]
test_netmiko_show.py::test_disable_paging PASSED                                                                                                                      [  8%]
test_netmiko_show.py::test_terminal_width PASSED                                                                                                                      [ 12%]
test_netmiko_show.py::test_ssh_connect PASSED                                                                                                                         [ 16%]
test_netmiko_show.py::test_ssh_connect_cm PASSED                                                                                                                      [ 20%]
test_netmiko_show.py::test_send_command_timing PASSED                                                                                                                 [ 24%]
test_netmiko_show.py::test_send_command_timing_no_cmd_verify SKIPPED                                                                                                  [ 28%]
test_netmiko_show.py::test_send_command PASSED                                                                                                                        [ 32%]
test_netmiko_show.py::test_send_command_no_cmd_verify SKIPPED                                                                                                         [ 36%]
test_netmiko_show.py::test_complete_on_space_disabled SKIPPED                                                                                                         [ 40%]
test_netmiko_show.py::test_send_command_textfsm SKIPPED (TextFSM/ntc-templates not supported on this platform)                                                        [ 44%]
test_netmiko_show.py::test_send_command_ttp SKIPPED (TTP template not existing for this platform)                                                                     [ 48%]
test_netmiko_show.py::test_send_command_genie SKIPPED (Genie not supported on this platform)                                                                          [ 52%]
test_netmiko_show.py::test_send_multiline_timing SKIPPED                                                                                                              [ 56%]
test_netmiko_show.py::test_send_multiline SKIPPED                                                                                                                     [ 60%]
test_netmiko_show.py::test_send_multiline_prompt SKIPPED                                                                                                              [ 64%]
test_netmiko_show.py::test_send_multiline_simple SKIPPED                                                                                                              [ 68%]
test_netmiko_show.py::test_base_prompt PASSED                                                                                                                         [ 72%]
test_netmiko_show.py::test_strip_prompt PASSED                                                                                                                        [ 76%]
test_netmiko_show.py::test_strip_command PASSED                                                                                                                       [ 80%]
test_netmiko_show.py::test_normalize_linefeeds PASSED                                                                                                                 [ 84%]
test_netmiko_show.py::test_clear_buffer PASSED                                                                                                                        [ 88%]
test_netmiko_show.py::test_enable_mode PASSED                                                                                                                         [ 92%]
test_netmiko_show.py::test_disconnect PASSED                                                                                                                          [ 96%]
test_netmiko_show.py::test_disconnect_no_enable SKIPPED                                                                                                               [100%]

========================================================================== short test summary info ==========================================================================
SKIPPED [1] test_netmiko_show.py:25: Not using SSH-keys
SKIPPED [1] test_netmiko_show.py:88: Skipped
SKIPPED [1] test_netmiko_show.py:106: Skipped
SKIPPED [1] test_netmiko_show.py:128: Skipped
SKIPPED [1] test_netmiko_show.py:149: TextFSM/ntc-templates not supported on this platform
SKIPPED [1] test_netmiko_show.py:171: TTP template not existing for this platform
SKIPPED [1] test_netmiko_show.py:211: Genie not supported on this platform
SKIPPED [1] test_netmiko_show.py:231: Skipped
SKIPPED [1] test_netmiko_show.py:247: Skipped
SKIPPED [1] test_netmiko_show.py:272: Skipped
SKIPPED [1] test_netmiko_show.py:296: Skipped
SKIPPED [1] test_netmiko_show.py:401: Skipped
====================================================================== 13 passed, 12 skipped in 22.91s ======================================================================

output from config test:

============================================================================ test session starts ============================================================================
platform linux -- Python 3.10.16, pytest-8.3.5, pluggy-1.5.0 -- /usr/bin/python3.10
cachedir: .pytest_cache
rootdir: /home/ticktock/netmiko
configfile: setup.cfg
collected 13 items                                                                                                                                                          

test_netmiko_config.py::test_ssh_connect PASSED                                                                                                                       [  7%]
test_netmiko_config.py::test_enable_mode PASSED                                                                                                                       [ 15%]
test_netmiko_config.py::test_config_mode PASSED                                                                                                                       [ 23%]
test_netmiko_config.py::test_exit_config_mode PASSED                                                                                                                  [ 30%]
test_netmiko_config.py::test_config_set PASSED                                                                                                                        [ 38%]
test_netmiko_config.py::test_config_set_generator PASSED                                                                                                              [ 46%]
test_netmiko_config.py::test_config_set_longcommand PASSED                                                                                                            [ 53%]
test_netmiko_config.py::test_config_hostname PASSED                                                                                                                   [ 61%]
test_netmiko_config.py::test_config_from_file SKIPPED                                                                                                                 [ 69%]
test_netmiko_config.py::test_config_error_pattern SKIPPED (No error_pattern defined.)                                                                                 [ 76%]
test_netmiko_config.py::test_banner SKIPPED (No banner defined.)                                                                                                      [ 84%]
test_netmiko_config.py::test_global_cmd_verify SKIPPED (No banner defined.)                                                                                           [ 92%]
test_netmiko_config.py::test_disconnect PASSED                                                                                                                        [100%]

========================================================================== short test summary info ==========================================================================
SKIPPED [1] test_netmiko_config.py:163: Skipped
SKIPPED [1] test_netmiko_config.py:175: No error_pattern defined.
SKIPPED [1] test_netmiko_config.py:209: No banner defined.
SKIPPED [1] test_netmiko_config.py:242: No banner defined.
======================================================================= 9 passed, 4 skipped in 59.45s =======================================================================