Projects deleted on the primary may not be deleted on the secondary due to sidekiq losing jobs

The following discussion from !2838 (merged) should be addressed:

• @nick.thomas started a discussion:

  A bug exists here - sidekiq can lose jobs, and if that happens, the repository will never be removed. Options:

  • Use execute instead of async_execute (slows down the project)
  • Add a project_registry.pending_delete field and schedule sidekiq jobs until the row goes away, signalling completion

  It's a pre-existing bug, so we can resolve it in a separate issue :)