ARTEMIS-6101 Add cluster credentials to clustered-grouping server2

Author: brusdev

examples/features/clustered/clustered-grouping/src/main/resources/activemq/server2/broker.xml

@@ -57,6 +57,9 @@ under the License.
          </discovery-group>
       </discovery-groups>
 
+      <cluster-user>my-cluster-user</cluster-user>
+      <cluster-password>my-cluster-password</cluster-password>
+
       <cluster-connections>
          <cluster-connection name="my-cluster">
             <connector-ref>netty-connector</connector-ref>