Display comments on commits in MR diffs
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=14444)
</details>
<!--IssueSummary end-->
It would be great to make it possible to display comments on commits in merge request diff if given line is up to date with commit.
We need this to simplify process of posting comments on commits from CI jobs.
It would be then easy to inline a CI output in MR diff automatically (like adding Rubocop offenses from Rubocop job to MR diff).
/cc @DouweM @ayufan @JobV @tmaczukin @dzaporozhets @markpundsack
issue