feat: add pathspec_error_handling input

[EndBug]

The PR adds the pathspec_error_handling input, which allows you to choose how the action handles pathspec errors from the git add and git rm commands.
The default behavior remains to ignore this kind of errors, but you can also choose to exit immediately or at the end.

Closes #251

[EndBug]

@Glidias Sorry for the long waiting time 😅
If you want to try out the new feature before I merge it to give some feedback, you can use EndBug/add-and-commit@feat/pathspec-error-handling. The docs are in the README of that branch.