Geo - Rename backfill service/worker

What does this MR do?

• Rename Geo::RepositoryBackfilService to Geo::RepositorySyncService
• Rename GeoBackfillWorker to GeoRepositorySyncWorker

Are there points in the code the reviewer needs to double check?

No.

Why was this MR needed?

Make the classes name more consistent with its behavior.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • 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 #2274 (closed)