Forbid commit messages patterns

See https://github.com/smarkets/marge-bot/issues/329

I'd suggest running it with MARGE_FORBID_COMMIT_MESSAGE="[fixup!.*, Apply .* suggestion\(s\) to .* file\(s\)]"

Or --forbid-commit-message 'fixup!.*' --forbid-commit-message 'Apply .* suggestion\(s\) to .* file\(s\)'.

Or in the config file:

forbid-commit-message:
  - fixup!.*
  - Apply .* suggestion\(s\) to .* file\(s\)

I've written a few unit tests and I've also verified that it works on a private project.