Snapshots on Share Replicas must be available through tenant visible APIs

Snapshots have the same granularity as Shares in Manila. Like replicas are just share instances behind the curtains, replica snapshots are snapshot instances. Since replication is mostly tenant facing, barring a few "administrator" APIs, we need new APIs to list/show the snapshots that are created on the replicas.

These APIs should be tagged ``experimental`` in the newton release

Note: You cannot snapshot a secondary; snapshots are taken on the primary and are replicated to the secondaries.