Fix memory request limit exmaples use the default namespace (#6979)

docs/tasks/configure-pod-container/memory-request-limit-2.yaml

@@ -2,6 +2,7 @@ apiVersion: v1
 kind: Pod
 metadata:
   name: memory-demo-2
+  namespace: mem-example
 spec:
   containers:
   - name: memory-demo-2-ctr

docs/tasks/configure-pod-container/memory-request-limit-3.yaml

@@ -2,6 +2,7 @@ apiVersion: v1
 kind: Pod
 metadata:
   name: memory-demo-3
+  namespace: mem-example
 spec:
   containers:
   - name: memory-demo-3-ctr

docs/tasks/configure-pod-container/memory-request-limit.yaml

@@ -2,6 +2,7 @@ apiVersion: v1
 kind: Pod
 metadata:
   name: memory-demo
+  namespace: mem-example
 spec:
   containers:
   - name: memory-demo-ctr