Destroy cache entries that are marked for deletion

In Additional API endpoints: Delete cache on regis... (#578680 - closed), we add API endpoints that allow the deletion of cache from an upstream and registry. In that issue, we mark the cache entries as pending deletion.

In this issue, we would like to make sure that the cache entries that are marked for deletion are actually deleted.

Maven reference:

• ee/app/workers/ee/dependency_proxy/cleanup_dependency_proxy_worker.rb
• ee/app/workers/ee/virtual_registries/packages/cache/destroy_orphan_entries_worker.rb