feat: add custom validation

[benediktziegler]

Description

This PR adds functionality to customise the commit message validation and to format the InvalidCommitMessageError to give better/more detailed feedback to the user.

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

The developer of a custom commitizen class can override the validate_commit_message and format_error_message methods to perform more complex commit message format checks then just a regex match and give more detailed feedback on failure.

Steps to Test This Pull Request

Run the the test_check_command_with_custom_validator_succeed and test_check_command_with_custom_validator_fail tests in test_check_command.py.

Additional context

This PR implements and fixes the comments from #648.
Cleaned up version of #1236

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (v4-11-0@701de0a). Learn more about missing BASE report.

Additional details and impacted files

@@            Coverage Diff             @@
##             v4-11-0    #1680   +/-   ##
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  Coverage           ?   98.68%           
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  Files              ?       60           
  Lines              ?     2655           
  Branches           ?        0           
==========================================
  Hits               ?     2620           
  Misses             ?       35           
  Partials           ?        0           

Flag	Coverage Δ
unittests	98.68% <100.00%> (?)

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[bearomorphism]

Just note that this file will probably be removed in #1657