[Feature flag] codequality_mr_diff_annotations - Enable code quality diff annotations on MR diff

Summary

This issue is to rollout inline code quality annotations on production, that is currently behind the codequality_mr_diff_annotations feature flag.

This is closely related to and expands on the codequality_mr_diff feature flag.

Owners

• Team: devopsverify grouptesting
• Most appropriate slack channel to reach out to: #g_testing
• Best individuals to reach out to: @mfluharty, @shampton
• PM: @jheimbuck_gl

Expectations

What are we expecting to happen?

Icons will appear next to lines in the MR diff when they introduce new code quality violations:

What might happen if this goes wrong?

We could break the MR diff page somehow 😬

What can we monitor to detect problems with this?

Keep a close eye on slack channels where people would report bugs (i.e. #is-this-known) when we enable it for the GitLab project

Rollout Steps

• Enable on staging (/chatops run feature set codequality_mr_diff_annotations true --staging)
• Test on staging
• Ensure that documentation has been updated: !63923 (merged)
• Enable on GitLab.com for individual groups/projects listed above and verify behaviour (/chatops run feature set --project=gitlab-org/gitlab codequality_mr_diff_annotations true)
• Enable on GitLab.com by running chatops command in #production (/chatops run feature set codequality_mr_diff_annotations true)
• Announce on the issue that the flag has been enabled
• Remove feature flag and add changelog entry: !65960 (merged)
• After the flag removal is deployed, clean up the feature flag by running chatops command in #production channel