What does this MR do?
Extract project#update_merge_requests to its own worker from GitPushService
I'd discarded to extract more code from the current
GitPushService#update_merge_requests method because I think the other parts of that method are not related with the updating of merge requests they are more related with hooks, and I think we can extract that from both services (GitPushService and GitTagPushService) to the same place in other PR
Are there points in the code the reviewer needs to double check?
Why was this MR needed?
Relates to #15463 (moved)
Screenshots (if relevant)
Does this MR meet the acceptance criteria?
CHANGELOG entry added
API support added
Added for this feature/bug
All builds are passing
Conform by the merge request performance guides
Conform by the style guides
Branch has no merge conflicts with
master(if it does - rebase it please)
Squashed related commits together