fix busybox image to 1.28 (issues with nslookup).

Changes where done with these commands:

reprec 'image: busybox(?!:)' 'image: busybox:1.28' */docs */examples
reprec -- '--image=busybox(?!:)' '--image=busybox:1.28' */docs */examples

Related issues:

 https://github.com/docker-library/busybox/issues/48
 https://github.com/kubernetes/kubernetes/issues/66924

content/en/docs/concepts/storage/ephemeral-volumes.md

@@ -107,7 +107,7 @@ metadata:
 spec:
   containers:
     - name: my-frontend
-      image: busybox
+      image: busybox:1.28
       volumeMounts:
       - mountPath: "/data"
         name: my-csi-inline-vol
@@ -158,7 +158,7 @@ metadata:
 spec:
   containers:
     - name: my-frontend
-      image: busybox
+      image: busybox:1.28
       volumeMounts:
       - mountPath: "/scratch"
         name: scratch-volume

content/en/docs/concepts/storage/volumes.md

@@ -251,7 +251,7 @@ metadata:
 spec:
   containers:
     - name: test
-      image: busybox
+      image: busybox:1.28
       volumeMounts:
         - name: config-vol
           mountPath: /etc/config
@@ -1128,7 +1128,7 @@ spec:
         fieldRef:
           apiVersion: v1
           fieldPath: metadata.name
-    image: busybox
+    image: busybox:1.28
     command: [ "sh", "-c", "while [ true ]; do echo 'Hello'; sleep 10; done | tee -a /logs/hello.txt" ]
     volumeMounts:
     - name: workdir1