feat: add support for Merge commit

[thoaionline]

Notes to reviewer

• The upper case in the message was intentional, it's the default message generated by git. This helps with the merge workflow (e.g. in private repos).
• Hided some non-critical input from the test suite

[thoaionline]

@thekaveman wysiwyg

[thekaveman]

Thanks for your suggestion @thoaionline!

I think we'd like to keep this hook small and simple, and focused on Conventional Commits use-cases. Since this hook only comes into play locally, you do also have the option of customizing the merge commit message to be "conventional" at that time:

git commit merge -m "feat: merge new feature to main"