[Snapshot Interop] Add Shallow Copy Snapshots list in Snapshot Repository Data

[harishbhakuni]

Describe the bug
During Snapshot Deletion, Today we are relying on repository setting to determine if we should use the new delete snapshots method which cleans up lock files as well or the old one. IF user enables shallow copy snapshot flag and creates multiple shallow copy snapshots and then disables flag and triggers deletion of those shallow copy snapshots, we will end up leaving stale shallow copy blobs belonging to those snapshots.

To Fix this, we need to add the list of Shallow Copy Snapshots in Repository Data. So that we don't rely just on the repository flag.

[gbbafna]

I would also think about making shallow copy as a static parameter in repo . That would make the code paths quite simple.

Existing user can delete the existing repo and reregister as a read-only repo with shallow snapshot as a static parameter

[harishbhakuni]

We need to fix this before supporting migration from remote backed indices to doc-rep indices (#12718). as we cannot anymore rely on not changing remote_store_index_shallow_copy repository setting.

[harishbhakuni]

@gbbafna ^^

[gbbafna]

Post this, we can make shallow snapshot a dynamic property of repository as well .