code: func (m *Manager) GetClientLabels(clientID string) (labels []string, err error) {
  	results := []struct{ Label string }{}
  	err = m.getClientsCollection().Find(bson.M{"clientid": clientID}).Select(bson.M{"label": 1}).All(&results)
  	labels = make([]string, len(results), len(results))
  	for i, value := range results {
  		labels[i] = value.Label
  	}
  	return
  }
docs: //GetClientLabels returns a list of labels for which there are apikeys registered for a specific client