Show author badge in comments

In addition to the badges showing the commenter's role (Contributor, Guest, Reporter, etc.), add a new Author badge to the left of those when the author of an issue, merge request, or epic comments.

This was behind a feature flag for a year (!) but that feature flag has been enabled by default in #250282 (closed). Thanks @TaehyeokKang!

Issues:

Merge requests:

Epics (don't yet show user role):