Add suggestion for missing merge request in changelog
When an MR IID is missing from the changelog entry, add a suggestion so that it's easy to fix. Test MRs:
- No MR IID: !33083 (closed)
- Correct MR IID: !33081 (closed)
- No
merge_request
line at all: !33082 (closed)
Closes #218752 (closed).
Edited by Sean McGivern