Increase parallelism of geo repository sync worker
What does this MR do?
Reuse the same logic from https://gitlab.com/gitlab-org/gitlab-ce/issues/29258 to schedule jobs to sync project repositories.
Why was this MR needed?
GeoRepositorySyncWorker fetches one repo at a time. With hundreds of thousands of projects, this is too slow and inefficient, especially if one repo is blocked for some reason.
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Documentation created/updated
- 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
What are the relevant issue numbers?
Closes #2742 (closed)