bump the stability level of apiserver_storage_size_bytes to STABLE

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

@@ -84,7 +84,7 @@ var (
 		},
 		[]string{"endpoint"},
 	)
-	storageSizeDescription   = compbasemetrics.NewDesc("apiserver_storage_size_bytes", "Size of the storage database file physically allocated in bytes.", []string{"cluster"}, nil, compbasemetrics.ALPHA, "")
+	storageSizeDescription   = compbasemetrics.NewDesc("apiserver_storage_size_bytes", "Size of the storage database file physically allocated in bytes.", []string{"cluster"}, nil, compbasemetrics.STABLE, "")
 	storageMonitor           = &monitorCollector{monitorGetter: func() ([]Monitor, error) { return nil, nil }}
 	etcdEventsReceivedCounts = compbasemetrics.NewCounterVec(
 		&compbasemetrics.CounterOpts{

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

@@ -197,7 +197,7 @@ func TestStorageSizeCollector(t *testing.T) {
 				return []Monitor{fakeEtcdMonitor{storageSize: 1e9}}, nil
 			},
 			err: nil,
-			want: `# HELP apiserver_storage_size_bytes [ALPHA] Size of the storage database file physically allocated in bytes.
+			want: `# HELP apiserver_storage_size_bytes [STABLE] Size of the storage database file physically allocated in bytes.
 			# TYPE apiserver_storage_size_bytes gauge
 			apiserver_storage_size_bytes{cluster="etcd-0"} 1e+09
 			`,

test/instrumentation/testdata/stable-metrics-list.yaml

@@ -309,6 +309,12 @@
   stabilityLevel: STABLE
   labels:
   - resource
+- name: apiserver_storage_size_bytes
+  help: Size of the storage database file physically allocated in bytes.
+  type: Custom
+  stabilityLevel: STABLE
+  labels:
+  - cluster
 - name: container_cpu_usage_seconds_total
   help: Cumulative cpu time consumed by the container in core-seconds
   type: Custom