Get `9-2-stable-ee` up to date with `ce/9-2-stable`

Background

• We didn't want to directly merge in ce/9-2-stable to 9-2-stable-ee, since that would cause a lot of conflicts that have already been fixed in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1837
• https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1837 had a green build yesterday (ef0b3a56), but wasn't merged in, and has since been updated against ee/master, and now has more pending conflicts to resolve.

What does this MR do?

Update 9-2-stable-ee to be up-to-date with 9-2-stable, by following these steps:

1. Create a branch 9-2-stable-upstream off 9-2-stable-ee

2. Merge ce_upstream with the latest ee/master commit that has been previously merged into ce_upstream (to guarantee a conflict-free merge) locally. Pick the merge commit (cherry-pick -m1) onto 9-2-stable-upstream

3. ce_upstream was branched off from ce/master at 6ce1df41 (found using git merge-base ce_upstream ce/master). Essentially 6ce1df41 is the latest CE commit for which ce_upstream contains conflict fixes.

4. Merge 6ce1df41 into 9-2-stable-upstream, resolving all conflicts with git checkout --ours <file>. This is safe, since "ours" contains all necessary conflict fixes from 2.

5. Merge 9-2-stable into 9-2-stable-upstream. There are conflicts (for changes made between 6ce1df41 and 9-2-stable's HEAD), as expected, which have been committed as-is for the moment.

Are there points in the code the reviewer needs to double check?

Are there any flaws with this strategy?