Add metrics of RunnerDeployment and HRA (#408)

* Add metrics of RunnerDeployment and HRA

* Use kube-state-metrics-style label names

controllers/metrics/runnerdeployment.go

@@ -0,0 +1,37 @@
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/summerwind/actions-runner-controller/api/v1alpha1"
+)
+
+const (
+	rdName      = "runnerdeployment"
+	rdNamespace = "namespace"
+)
+
+var (
+	runnerDeploymentMetrics = []prometheus.Collector{
+		runnerDeploymentReplicas,
+	}
+)
+
+var (
+	runnerDeploymentReplicas = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "runnerdeployment_spec_replicas",
+			Help: "replicas of RunnerDeployment",
+		},
+		[]string{rdName, rdNamespace},
+	)
+)
+
+func SetRunnerDeployment(rd v1alpha1.RunnerDeployment) {
+	labels := prometheus.Labels{
+		rdName:      rd.Name,
+		rdNamespace: rd.Namespace,
+	}
+	if rd.Spec.Replicas != nil {
+		runnerDeploymentReplicas.With(labels).Set(float64(*rd.Spec.Replicas))
+	}
+}