code: func PreRegisterDialerMetrics(dialerName string) {
  	dialerAttemptedTotal.WithLabelValues(dialerName)
  	dialerConnEstablishedTotal.WithLabelValues(dialerName)
  	for _, reason := range []failureReason{failedTimeout, failedResolution, failedConnRefused, failedUnknown} {
  		dialerConnFailedTotal.WithLabelValues(dialerName, string(reason))
  	}
  	dialerConnClosedTotal.WithLabelValues(dialerName)
  }
docs: // preRegisterDialerMetrics pre-populates Prometheus labels for the given dialer name, to avoid Prometheus missing labels issue.