Implement workhorse acceleration for project imports

In the context of &1802 it was discovered that project imports (from gitlab exports) behave differently when triggered from the web interface or API.

Only in the first case, it gets the benefits of workhorse disk acceleration.

But in both cases is broken on a ~"Cloud Native" installations because of web and sidekiq sharing files with filesystem.

Implementing a workhorse object storage acceleration will fix both problems at once.