Making _cat/allocation API use indexLevelStats (#15790)

Signed-off-by: Harsh Garg <[email protected]>

Author: gargharsh3134

release-notes/opensearch.release-notes-2.17.0.md

@@ -52,6 +52,7 @@
 - Reset DiscoveryNodes in all transport node actions request ([#15131](https://github.com/opensearch-project/OpenSearch/pull/15131))
 - MultiTermQueries in keyword fields now default to `indexed` approach and gated behind cluster setting ([#15637](https://github.com/opensearch-project/OpenSearch/pull/15637))
 - Adding WithFieldName interface for QueryBuilders with fieldName ([#15705](https://github.com/opensearch-project/OpenSearch/pull/15705))
+- Making _cat/allocation API use indexLevelStats ([#15292](https://github.com/opensearch-project/OpenSearch/pull/15292))
 - Static RemotePublication setting added, removed experimental feature flag ([#15478](https://github.com/opensearch-project/OpenSearch/pull/15478))
 -  [Remote Publication] Upload incremental cluster state on master re-election ([#15145](https://github.com/opensearch-project/OpenSearch/pull/15145))
 

server/src/main/java/org/opensearch/rest/action/cat/RestAllocationAction.java

@@ -101,6 +101,7 @@ public void processResponse(final ClusterStateResponse state) {
                 statsRequest.clear()
                     .addMetric(NodesStatsRequest.Metric.FS.metricName())
                     .indices(new CommonStatsFlags(CommonStatsFlags.Flag.Store));
+                statsRequest.indices().setIncludeIndicesStatsByLevel(true);
 
                 client.admin().cluster().nodesStats(statsRequest, new RestResponseListener<NodesStatsResponse>(channel) {
                     @Override