code: public ListInstancesResponse listInstances(String clusterId, String instanceGroupId) {
          return listInstances(new ListInstancesRequest().withClusterId(clusterId).withInstanceGroupId(instanceGroupId));
      }
docs: List the instances belonging to the target instance in the BMR cluster.
  
  @param clusterId the ID of target BMR cluster.
  @param instanceGroupId the ID of target instance group.
  @return The response containing a list of Instance objects.