code: func (s *IndicesStatsService) Metric(metric ...string) *IndicesStatsService {
  	s.metric = append(s.metric, metric...)
  	return s
  }
docs: // Metric limits the information returned the specific metrics. Options are:
  // docs, store, indexing, get, search, completion, fielddata, flush, merge,
  // query_cache, refresh, suggest, and warmer.