Add test ensure we can execute update requests in mixed cluster

Relates #42596

Author: dnhatn

qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/RecoveryIT.java

@@ -567,4 +567,22 @@ private void ensureGlobalCheckpointSynced(String index) throws Exception {
                 });
         }, 60, TimeUnit.SECONDS);
     }
+
+    /** Ensure that we can always execute update requests regardless of the version of cluster */
+    public void testUpdateDoc() throws Exception {
+        final String index = "test_update_doc";
+        if (CLUSTER_TYPE == ClusterType.OLD) {
+            Settings.Builder settings = Settings.builder()
+                .put(IndexMetaData.INDEX_NUMBER_OF_SHARDS_SETTING.getKey(), 1)
+                .put(IndexMetaData.INDEX_NUMBER_OF_REPLICAS_SETTING.getKey(), 2);
+            createIndex(index, settings.build());
+        }
+        ensureGreen(index);
+        indexDocs(index, 0, 10);
+        for (int i = 0; i < 10; i++) {
+            Request update = new Request("POST", index + "/_update/" + i);
+            update.setJsonEntity("{\"doc\": {\"f\": " + randomNonNegativeLong() + "}}");
+            client().performRequest(update);
+        }
+    }
 }