feat(postgres): Enable security enhancements

This patch enables read-only filesystems and no-new-privileges for all
postgres databases managed by the zalando postgres operator.

infrastructure/postgres/release.yaml

@@ -22,3 +22,5 @@ spec:
     # Required due to OpenShift magic
     securityContext:
       runAsUser: null
+      readOnlyRootFilesystem: true
+      allowPrivilegeEscalation: false