[SnapshotV2] Snapshot Status API changes

[ltaragi]

Is your feature request related to a problem? Please describe

As part of V2 snapshots, we require optimisations for the Snapshot Status API

Describe the solution you'd like

• Allow index filter in the status API if the request contains only one snapshot name. Thus, the status API response will only consist of the specified indices in the filter (if any). Throw IndexNotFoundException in case an index name is not found in the provided snapshot.
• For shallow snapshots of type V2, the file count and size stats are 0 at all levels.
• For other snapshots: The status API call works only if the total number of shards across the requested resources (snapshots or the indices of a particular snapshot) is less than a certain amount determined by the cluster setting snapshot.max_shards_allowed_in_status_api

Related component

Storage:Snapshots

Describe alternatives you've considered

No response

Additional context

No response

[ltaragi]

The primary store size at the time of snapshot creation can be persisted in SnapshotInfo.java, and used to return the total size of the snapshot in bytes in the status response for shallow V2 snapshots.