As a user, I can sync from static files in the v2 API layout
The only known blocker to doing this is the manifest digest, which is available via the Docker-Content-Digest header when doing a pull/sync from the upstream registry. If the plugin knew how to calculate that, it could sync from static files.
This is important, because crane will implement v2 pull by redirecting manifest GET requests to static file service like the CDN, which will not know how to return the optional Docker-Content-Digest header. Pulp should be able to sync from itself.