[pre-commit-hook] Automatically update the baseline

[KevinHock]

When no secrets are present, that is.

(pre_commit_hook.py)
Do not raise exception when baseline out-of-date
Replace baseline version/plugins with the current ones.
Replaced raise_exception_if_baseline_version_is_outdated with if statement
Renamed raise_exception_if_baseline_file_is_not_up_to_date to raise_exception_if_baseline_file_is_unstaged
Improve comment

(core/secrets_collection.py)
Make version not required for baseline's any more

(tests/pre_commit_hook_test.py):
Replaced test_fails_if_baseline_version_is_outdated with test_that_baseline_gets_updated

Clean up:
(core/usage.py)
Static list into a tuple
(core/baseline.py)
initialize() docstring accurate
Renamed update_baseline_with_removed_secrets to trim_baseline_of_removed_secrets
Renamed git_files to files_to_scan
Fix typo (propogate -> propagate)