fixed issues with schema of network policy

also fixed encoding of matahLabels. Now using json format so that it
also works for empty maps.

cmd/policygen/templates/netpol/namespace/dns.yaml

@@ -0,0 +1,19 @@
+{{- if not .Open }}
+
+---
+kind: NetworkPolicy
+apiVersion: networking.k8s.io/v1
+metadata:
+  name: allow-dns-in-namespace
+  namespace: {{ .Name }}
+spec:
+  podSelector: {}
+  policyTypes:
+    - Egress
+  egress:
+    - ports:
+        - port: 53
+          protocol: TCP
+        - port: 53
+          protocol: UDP
+{{- end }}