Improve upstream notification to post to MR instead of commit
- We'll now post the upstream comment on MRs only.
- All notifications will go into the same comment.
Example of a first-time comment:
Example of a second notification:
Example of a third notification:
This has been tested in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/85724#note_927391125.
Related to https://gitlab.com/gitlab-org/gitlab/-/issues/350478#note_921161776.
Edited by George Koltsov