Added transport action for bulk async shard fetch for primary shards

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Allow mmap to use new JDK-19 preview APIs in Apache Lucene 9.4+ ([#5151](https://github.com/opensearch-project/OpenSearch/pull/5151))
 - Add events correlation engine plugin ([#6854](https://github.com/opensearch-project/OpenSearch/issues/6854))
 - Add support for ignoring missing Javadoc on generated code using annotation ([#7604](https://github.com/opensearch-project/OpenSearch/pull/7604))
+- Add PSA transport action for bulk async fetch of shards ([#5098](https://github.com/opensearch-project/OpenSearch/issues/5098))
 
 ### Dependencies
 - Bump `log4j-core` from 2.18.0 to 2.19.0
@@ -44,7 +45,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Change http code for DecommissioningFailedException from 500 to 400 ([#5283](https://github.com/opensearch-project/OpenSearch/pull/5283))
 - Improve summary error message for invalid setting updates ([#4792](https://github.com/opensearch-project/OpenSearch/pull/4792))
 - Pass localNode info to all plugins on node start ([#7919](https://github.com/opensearch-project/OpenSearch/pull/7919))
-
+- Modified the existing async shard fetch transport action to use the helper functions added for bulk fetching ([#5098](https://github.com/opensearch-project/OpenSearch/issues/5098))
 ### Deprecated
 
 ### Removed

server/src/main/java/org/opensearch/gateway/AsyncShardsFetchPerNode.java

@@ -0,0 +1,32 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.gateway;
+
+import org.opensearch.action.ActionListener;
+import org.opensearch.action.support.nodes.BaseNodeResponse;
+import org.opensearch.action.support.nodes.BaseNodesResponse;
+import org.opensearch.cluster.node.DiscoveryNode;
+import org.opensearch.common.lease.Releasable;
+import org.opensearch.index.shard.ShardId;
+
+import java.util.Map;
+
+/**
+ * This class is responsible for fetching shard data from nodes. It is analogous to AsyncShardFetch class since it fetches
+ * the data in asynchronous manner too.
+ * @param <T>
+ */
+public abstract class AsyncShardsFetchPerNode<T extends BaseNodeResponse> implements Releasable {
+    /**
+     * An action that lists the relevant shard data that needs to be fetched.
+     */
+    public interface Lister<NodesResponse extends BaseNodesResponse<NodeResponse>, NodeResponse extends BaseNodeResponse> {
+        void list(DiscoveryNode[] nodes, Map<ShardId, String> shardsIdMap, ActionListener<NodesResponse> listener);
+    }
+}