storage: root directory directly on cloud storage

[rchincha]

Is your feature request related to a problem? Please describe.

If we want to support a stateless zot (helps for clustering) but also support dedupe, then we cannot have anything on instance-local private storage. Even the dedupe cache should be on shared cloud storage.

• [ ] #667
• [ ] https://github.com/chofnar/zot/pull/18

[rchincha]

This need investigation/evaluation first.

[rchincha]

@chofnar Pls. take @peusebiu's help since he is the feature owner of this area.

[andaaron]

In review.