fix(namespace-configuration): Try to solve accumulating namespace

This patch may helps to resolve the "accumulating resources from 'postgres'" error

infrastructure/namespace-configuration/kustomization.yaml

 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
-namespace: zalando-postgres
+namespace: namespace-configuration-operator
 resources:
 - namespace.yaml
 - subscription.yaml

infrastructure/namespace-configuration/namespace.yaml

@@ -2,3 +2,5 @@ apiVersion: v1
 kind: Namespace
 metadata:
   name: namespace-configuration-operator
+  labels:
+    name: namespace-configuration-operator