Remove the backoff delay from Geo repository sync

What does this MR do?

Remove the backoff delay from Geo::RepositorySyncWorker

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

Why was this MR needed?

With the backoff delay, the worker - iterating every second - enqueues 25 jobs in a burst, which sit and do nothing for 5 minutes. This blocks the worker from doing anything else for that time. The jobs themselves are processed almost immediately once the timeout expires, leading to long periods of complete inactivity.

Keeping a low max_capacity while removing the backoff delay allows us to process jobs at a much higher rate whilst never going above the defined concurrency limit, so limiting load on the primary.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #3453 (closed)