Idea: Additional conformance checks for merge requests

• There should be a check for the Signed-off-by tag in commit messages.
  • Add documentation that this is required.
• Code formatting according to the rules of black should be enforced.
  • black versions should be consistent throughout project (e.g., local pre-commit and in CI pipeline)
  • at the moment, the code doesn't conform (make it conformant)
• Nice to have: check rules that are enforced in pre-commit (for consistency)
• To be consistent with #555, a changelog update should happen Hint: Changelog update will happen with the Gitflow + Towncrier update
• Gitlab code coverage visualization could be used to aid reviewers. See https://docs.gitlab.com/ee/ci/testing/test_coverage_visualization.html#python-example.