Prepare 12.2.1 release

Release issue: gitlab-org/release/tasks#927 (closed)

Summary

This MR prepares 12-2-stable for 12.2.1.

Automated cherry-picking

Merge requests labeled ~"Pick into 12.2" should be automatically picked into both the CE and EE prepration MRs using the following ChatOps command:

# In Slack
/chatops run release merge 12.2.1