@Override
  public DataNodeWrapper getDataNodeWrapper(final int index) {
    return dataNodeWrapperList.get(index);
  }
Get connection to ConfigNode-Leader in ClusterIT environment

<p>Notice: The caller should always use try-with-resource to invoke this interface in order to
return client to ClientPool automatically

@return {@link SyncConfigNodeIServiceClient} that connects to the ConfigNode-Leader
integration-test/src/main/java/org/apache/iotdb/it/env/cluster/env/AbstractEnv.java