add some documentation around the metrics stability migration changes for clarity

pkg/ssh/ssh.go

@@ -46,6 +46,14 @@ import (
 	"k8s.io/klog"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	tunnelOpenCounter = metrics.NewCounter(
 		&metrics.CounterOpts{

staging/src/k8s.io/apiserver/pkg/audit/metrics.go

@@ -29,6 +29,14 @@ const (
 	subsystem = "apiserver_audit"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	eventCounter = metrics.NewCounter(
 		&metrics.CounterOpts{

staging/src/k8s.io/apiserver/pkg/authentication/request/x509/x509.go

@@ -31,6 +31,14 @@ import (
 	"k8s.io/component-base/metrics/legacyregistry"
 )
 
+/*
+ * By default, the following metric is defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var clientCertificateExpirationHistogram = metrics.NewHistogram(
 	&metrics.HistogramOpts{
 		Namespace: "apiserver",

staging/src/k8s.io/apiserver/pkg/endpoints/filters/authentication.go

@@ -32,6 +32,14 @@ import (
 	"k8s.io/klog"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	authenticatedUserCounter = metrics.NewCounterVec(
 		&metrics.CounterOpts{

staging/src/k8s.io/apiserver/pkg/endpoints/metrics/metrics.go

@@ -52,6 +52,14 @@ const (
 	APIServerComponent string = "apiserver"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	// TODO(a-robinson): Add unit tests for the handling of these metrics once
 	// the upstream library supports it.

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go

@@ -45,6 +45,14 @@ import (
 	utiltrace "k8s.io/utils/trace"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	initCounter = metrics.NewCounterVec(
 		&metrics.CounterOpts{

staging/src/k8s.io/apiserver/pkg/storage/etcd3/metrics/metrics.go

@@ -24,6 +24,14 @@ import (
 	"k8s.io/component-base/metrics/legacyregistry"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	etcdRequestLatency = compbasemetrics.NewHistogramVec(
 		&compbasemetrics.HistogramOpts{

staging/src/k8s.io/apiserver/pkg/storage/value/metrics.go

@@ -32,6 +32,14 @@ const (
 	subsystem = "storage"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	transformerLatencies = metrics.NewHistogramVec(
 		&metrics.HistogramOpts{

staging/src/k8s.io/kube-aggregator/pkg/controllers/status/metrics.go

@@ -21,6 +21,14 @@ import (
 	"k8s.io/component-base/metrics/legacyregistry"
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	unavailableCounter = metrics.NewCounterVec(
 		&metrics.CounterOpts{

staging/src/k8s.io/legacy-cloud-providers/gce/token_source.go

@@ -41,6 +41,14 @@ const (
 	tokenURLBurst = 3
 )
 
+/*
+ * By default, all the following metrics are defined as falling under
+ * ALPHA stability level https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20190404-kubernetes-control-plane-metrics-stability.md#stability-classes)
+ *
+ * Promoting the stability level of the metric is a responsibility of the component owner, since it
+ * involves explicitly acknowledging support for the metric across multiple releases, in accordance with
+ * the metric stability policy.
+ */
 var (
 	getTokenCounter = metrics.NewCounter(
 		&metrics.CounterOpts{