Initial revision of merge request approval settings page for CTRT
Wraps up the end of #324948 (closed) (!) by revising the newly-created https://docs.gitlab.com/ee/user/project/merge_requests/approvals/settings.html for CTRT, clarity, completeness. Fixes inbound links I've found so far, but I have a bad feeling I'll find UI links that need repair, too. I'll repair those at the end, to keep the pipeline quick for the majority of the edits.
Related links
- Closes #324948 (closed)