feat(mointoring): Add monitoring network access label

This patch adds a new label to the monitoring namespace, that is
supposed to be used as part of network policies to grant network access
to the namespaces that want to be monitored.

This should help to properly confine the container networking.

infrastructure/monitoring/namespace.yaml

@@ -5,3 +5,4 @@ metadata:
   labels:
     name: monitoring-system
     kyverno.shivering-isles.com/class: "system"
+    monitoring.shivering-siles.com/network-access-required: "true"