add local plugin (#4262)

* add local plugin

See: #4260

Signed-off-by: Miek Gieben <miek@miek.nl>

* stickler bot

Signed-off-by: Miek Gieben <miek@miek.nl>

* See Also

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/local/metrics.go

@@ -0,0 +1,18 @@
+package local
+
+import (
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	// LocalhostCount report the number of times we've seen a localhost.<domain> query.
+	LocalhostCount = promauto.NewCounter(prometheus.CounterOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "local",
+		Name:      "localhost_requests_total",
+		Help:      "Counter of localhost.<domain> requests.",
+	})
+)