update apiserver-identity KEP with metrics

keps/sig-api-machinery/1965-kube-apiserver-identity/README.md

@@ -115,6 +115,39 @@ The refresh rate, lease duration will be configurable through kube-apiserver
 flags. The resync period will be configurable through a kube-controller-manager
 flag.
 
+Each kube-apiserver with expose the following metrics for its own ID:
+
+```go
+  uptime := metrics.NewGaugeVec(
+		&metricsGaugeOpts{
+			Namespace:      "apiserver",
+			Subsystem:      "identity",
+			Name:           "lease_uptime_seconds",
+			Help:           "Lease uptime seconds, labeled by the kube-apiserver ID in the Lease object, show the uptime of the Lease",
+			StabilityLevel: metrics.ALPHA,
+		},
+		[]string{"name"},
+	success := metrics.NewCounterVec(
+		&metrics.CounterOpts{
+			Namespace:      "apiserver",
+			Subsystem:      "identity",
+			Name:           "lease_success_count",
+			Help:           "Lease success count, labeled by the kube-apiserver ID in the Lease object, counts the number of success renewing a Lease",
+			StabilityLevel: metrics.ALPHA,
+		},
+		[]string{"name"},
+	)
+  failures := metrics.NewCounterVec(
+		&metrics.CounterOpts{
+			Namespace:      "apiserver",
+			Subsystem:      "identity",
+			Name:           "lease_failure_count",
+			Help:           "Lease failure count, labeled by the kube-apiserver ID in the Lease object, counts the number of failures to renew a Lease",
+			StabilityLevel: metrics.ALPHA,
+		},
+ 		[]string{"name"},
+```
+
 ### Test Plan
 
   - integration test for creating the Namespace and the Lease on kube-apiserver