Allow clients overriding the BaseCommitizen object to have more custom commit message validation beyond just matching a regex schema. This lets clients have custom error messages and more intelligent pattern matching.

Description

This change lets users add certain things like bad word filters or more intelligent task ID listing (for example, make sure one or more IDs appears in the commit message, and in no particular order).

Checklist

• Add test cases to all the changes you introduce
• Run./scripts/format and./scripts/test locally to ensure this change passes linter check and test
• Test the changes on the local machine manually
• Update the documentation for the changes

Expected behavior

Overridevalidate_commit orvalidate_commits inBaseCommitizen for commit validation functions that are expressible in Python, and not just by a regular expression.

Steps to Test This Pull Request

Run thetest_check_custom_validation_succeeds andtest_check_custom_validation_fails test cases intests/commands/test_check_command.py.

Additional context

I noticed during my development that thetest_check_command_with_empty_range case was failing with the error:

commitizen.exceptions.GitCommandError: fatal: ambiguous argument 'master..master': unknown revision or path not in the working tree.

instead of generating its expected output. I did my best to make sure that this failure wasn't related to my changes, since it also reproduced when I ran the test suite againstmaster. It could just be an issue with my local environment.