Use apps/v1 API group whenever possible (#8055)

The use of extensions/v1beta1, apps/v1beta1 and apps/v1beta2 API
groups should be discouraged.

Closes: #8049

docs/user-guide/replicasets/frontend.yaml

@@ -1,22 +1,17 @@
-apiVersion: extensions/v1beta1
+apiVersion: apps/v1
 kind: ReplicaSet
 metadata:
   name: frontend
-  # these labels can be applied automatically
-  # from the labels in the pod template if not set
-  # labels:
-    # app: guestbook
-    # tier: frontend
+  labels:
+    app: guestbook
+    tier: frontend
 spec:
   # this replicas value is default
   # modify it according to your case
   replicas: 3
-  # selector can be applied automatically
-  # from the labels in the pod template if not set,
-  # but we are specifying the selector here to
-  # demonstrate its usage.
   selector:
     matchLabels:
+      app: guestbook
       tier: frontend
     matchExpressions:
       - {key: tier, operator: In, values: [frontend]}

docs/user-guide/replicasets/redis-slave.yaml

@@ -1,23 +1,20 @@
-apiVersion: extensions/v1beta1
+apiVersion: apps/v1
 kind: ReplicaSet
 metadata:
   name: redis-slave
-  # these labels can be applied automatically
-  # from the labels in the pod template if not set
-  # labels:
-  #   app: redis
-  #   role: slave
-  #   tier: backend
+  labels:
+    app: redis
+    role: slave
+    tier: backend
 spec:
   # this replicas value is default
   # modify it according to your case
   replicas: 2
-  # selector can be applied automatically
-  # from the labels in the pod template if not set
-  # selector:
-  #   app: guestbook
-  #   role: slave
-  #   tier: backend
+  selector:
+    matchLabels:
+      app: redis
+      role: slave
+      tier: backend
   template:
     metadata:
       labels: