[Discuss] [Remote Store] Supporting multiple remote stores per index

[sachinpkale]

Is your feature request related to a problem? Please describe.
Currently, we support providing a repository name while creating a remote store enabled index. A repository points to a remote store and with this setting, only one remote store can be configured for a given index.
Sample payload:

{
  "settings": {
    "index": {
      "number_of_shards": 1,
      "number_of_replicas": 0,
      "replication": {
        "type": "SEGMENT"
      },
      "remote_store": {
        "enabled": true,
        "repository": "my-repo-1"
      }
    }
  }
}

In this issue, we want to discuss potential requirement of supporting multiple remote stores for an index.
One thing to note: Decision to support single vs multi repositories should not change the existing API contract. It can be handled in the same way _snapshot/_restore API handles indices:

OpenSearch/server/src/main/java/org/opensearch/action/admin/cluster/snapshots/restore/RestoreSnapshotRequest.java

Lines 493 to 500 in bff9d0f

	if (name.equals("indices")) {
	if (entry.getValue() instanceof String) {
	indices(Strings.splitStringByCommaToArray((String) entry.getValue()));
	} else if (entry.getValue() instanceof ArrayList) {
	indices((ArrayList<String>) entry.getValue());
	} else {
	throw new IllegalArgumentException("malformed indices section, should be an array of strings");
	}

[sachinpkale]

@dblock @Bukhtawar