Add javadoc

Signed-off-by: Sooraj Sinha <soosinha@amazon.com>

server/src/main/java/org/opensearch/gateway/remote/ClusterMetadataManifest.java

@@ -996,11 +996,4 @@ public String toString() {
                 + '}';
         }
     }
-
-    // TODO https://github.com/opensearch-project/OpenSearch/pull/14089
-    public static class ClusterStateDiffManifest {
-        public String getFromStateUUID() {
-            return null;
-        }
-    }
 }

server/src/main/java/org/opensearch/gateway/remote/ClusterStateDiffManifest.java

@@ -0,0 +1,22 @@
+/*
+ * 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.remote;
+
+/**
+ * Manifest of diff between two cluster states
+ *
+ * @opensearch.internal
+ */
+public class ClusterStateDiffManifest {
+
+    // TODO https://github.com/opensearch-project/OpenSearch/pull/14089
+    public String getFromStateUUID() {
+        return null;
+    }
+}

server/src/main/java/org/opensearch/gateway/remote/model/RemoteClusterStateManifestInfo.java

@@ -10,6 +10,9 @@
 
 import org.opensearch.gateway.remote.ClusterMetadataManifest;
 
+/**
+ * A class encapsulating the cluster state manifest and its remote uploaded path
+ */
 public class RemoteClusterStateManifestInfo {
 
     private final ClusterMetadataManifest clusterMetadataManifest;