code: func (c Metrics) Describe(ch chan<- *prometheus.Desc) {
  	ch <- c.TotalPushCount
  	ch <- c.IosSuccess
  	ch <- c.IosError
  	ch <- c.AndroidSuccess
  	ch <- c.AndroidError
  	ch <- c.QueueUsage
  }
docs: // Describe returns all possible prometheus.Desc