Better docs for standard topology labels

As per KEP 1659, topology labels are now more formalized.  Move away
from the older `failure-domain.beta` names ands use `topology` names
instead.

content/en/examples/pods/pod-with-pod-affinity.yaml

@@ -12,7 +12,7 @@ spec:
             operator: In
             values:
             - S1
-        topologyKey: failure-domain.beta.kubernetes.io/zone
+        topologyKey: topology.kubernetes.io/zone
     podAntiAffinity:
       preferredDuringSchedulingIgnoredDuringExecution:
       - weight: 100
@@ -23,7 +23,7 @@ spec:
               operator: In
               values:
               - S2
-          topologyKey: failure-domain.beta.kubernetes.io/zone
+          topologyKey: topology.kubernetes.io/zone
   containers:
   - name: with-pod-affinity
     image: k8s.gcr.io/pause:2.0