feat: introduce compatibility with native namespace packages

[kiraksi]

This PR:

• Similar to: feat: Introduce compatibility with native namespace packages python-bigquery#1720
• Integrates native namespace package for google and removes the usage of pkg_resource and pkgutil
• Instead of using pkg_resource in tests we have added importlib as a extra dependency to handle version checking
• Thus, setuptools package is no longer needed at runtime

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Fixes #705 🦕

[parthea]

There is an upcoming release freeze. This should be merged after the release freeze ends on November 29th.

[parthea]

LGTM, please could you also remove usage of pkg_resources here? Please feel free to make the change in this PR or a separate PR. This should allow us to close #482

python-bigquery-storage/tests/unit/test_reader_v1_arrow.py

Line 23 in 20b57c2

import pkg_resources

[kiraksi]

LGTM, please could you also remove usage of pkg_resources here? Please feel free to make the change in this PR or a separate PR. This should allow us to close #482

python-bigquery-storage/tests/unit/test_reader_v1_arrow.py

Line 23 in 20b57c2

import pkg_resources

Edit: Will be done in this PR

[parthea]

Added minor observations. Otherwise LGTM

[parthea]

We also need to migrate setup.py to use setuptoolsfind_namespace_packages(.. instead of setuptools.PEP420PackageFinder.find()