plugin/reload: Add metrics (#2922)

* Issue 2920
- Add failed reload counter metrics

* typo fix

* Requested Changes

plugin/reload/metrics.go

@@ -0,0 +1,17 @@
+package reload
+
+import (
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Metrics for the reload plugin
+var (
+	FailedCount = prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "reload",
+		Name:      "failed_count_total",
+		Help:      "Counter of the number of failed reload attempts.",
+	})
+)