Adding missing deployment labels (#9012)

content/en/docs/tutorials/stateless-application/guestbook/frontend-deployment.yaml

@@ -2,6 +2,8 @@ apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
 kind: Deployment
 metadata:
   name: frontend
+  labels:
+    app: guestbook
 spec:
   selector:
     matchLabels:

content/en/docs/tutorials/stateless-application/guestbook/redis-master-deployment.yaml

@@ -2,6 +2,8 @@ apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
 kind: Deployment
 metadata:
   name: redis-master
+  labels:
+    app: redis
 spec:
   selector:
     matchLabels:

content/en/docs/tutorials/stateless-application/guestbook/redis-slave-deployment.yaml

@@ -2,6 +2,8 @@ apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
 kind: Deployment
 metadata:
   name: redis-slave
+  labels:
+    app: redis
 spec:
   selector:
     matchLabels: