Ability to start discussions on commit message

Problem to solve

Sometimes we need to point to errors in commit message. So it will be useful to have ability to start discussion on it (on whole cm, or maybe on certain lines of it). In current version we should manually specify, that opened thread relates to cm, and thereafter it misses cool features of code discussions (it is not marked as outdated/changed and so on).

Intended users

Any reviewer in company where cm matters.