Known heavy uses of Redis are triaged with the appropriate stage group

Exit criterion for &265.

Also included are the following from gitlab-org/gitlab

• https://gitlab.com/gitlab-org/gitlab/-/issues/219071 : session:lookup:ip:gitlab redis set is not cleared on persistent use
• gitlab-org/gitlab#225600 (closed) : MR discussion diffs persists and reads too much data from Redis

Once all the blocking issues are done, this can be closed!