code: func (s *ClusterRerouteService) Metric(metrics ...string) *ClusterRerouteService {
  	s.metrics = append(s.metrics, metrics...)
  	return s
  }
docs: // Metric limits the information returned to the specified metric.
  // It can be one of: "_all", "blocks", "metadata", "nodes", "routing_table", "master_node", "version".
  // Defaults to all but metadata.