Add namespace manifest

Author: MikeRayMSFT

samples/features/high availability/Kubernetes/sample-manifest-files/operator.yaml

@@ -1,3 +1,7 @@
+apiVersion:v1
+kind: Namespace
+metadata: {name: ag1}
+---
 apiVersion: v1
 kind: ServiceAccount
 metadata: {name: mssql-operator, namespace: ag1}