[DOC] Update Snapshot Restore API Documentation with Snapshot Interoperability w/ Remote Store Changes.

[harishbhakuni]

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Tell us about your request. Provide a summary of the request and all versions that are affected.
For our new feature Snapshot Interoperability w/ Remote Store, we need to update the request fields for Restore Snapshot API with a new field remote_store_index_shallow_copy:

Parameter	Data type	Description
source_remote_store_repository	String	Remote Store Repository name of source indices which are being restored, if it was modified after snapshot creation. Optional.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
For testing, follow the steps mentioned in this doc to create shallow copy snapshot: #4599.
After taking snapshot, change repository name for remote store repo. Now, normal snapshot would fail for remote store indices, but if the updated repository name is passed as shown in below example, snapshot restore would work fine.

Sample Request:

curl -X POST "localhost:9200/_snapshot/shallowCopyRepository/shallow_snap/_restore?wait_for_completion=true" -H 'Content-Type: application/json' -d'
{
  "indices": "testidx-dr",
  "rename_pattern": "(.+)",
  "rename_replacement": "restored_shallow-$0",
  "source_remote_store_repository": "remoteStoreRepoUpdated"
}
'