Allow discussions of commits and commit messages in merge requests.

Proposal

When reviewing merge requests it's currently possible to go commit by commit, which is great. Unfortunately, while you can start a discussion on a specific line in a specific commit, it is not possible to start a discussion about the commit in general, nor about the commit title or commit message body.

What I would like to have is the ability to comment on the commit in general.

I did a bad mock-up by copy pasting already existing UI elements to show what I mean:

Usecases

We have standards for commit messages, and for purposes of git blame and git bisect I like to keep the commit qualities at an acceptable level (which also includes having usable commit messages). The only way to do this currently is to open a discussion on the level of the merge request, copy in the commit messages as say quotes and then give feedback there. With the above it would be much cleaner, faster and most importantly: easier to track for somebody actually needing to make the changes.