fix(monitoring): revert mutation and validation webhook change

This patch reverts the commit 0176ef91
since it limits the actual usage of prometheus-operator resources to the
mentioned namespaces, which removes them from autodiscovery and alike.

infrastructure/monitoring/release.yaml

@@ -141,10 +141,6 @@ data:
       enabled: true
     prometheusOperator:
       enabled: true
-      namespaces:
-        releaseNamespace: true
-        additional:
-          - kube-system
       admissionWebhooks:
         failurePolicy: Fail
         enabled: true