fix: re-enable admission webhooks for prometheus-operator

The operator deployment mounts the admission TLS secret regardless
of admissionWebhooks.enabled. Disabling webhooks prevents the secret
from being created while the operator still expects it, causing a
FailedMount and the pod stuck in ContainerCreating.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: pedjak

testdata/prometheus/values.yaml

@@ -26,6 +26,8 @@ defaultRules:
 prometheusOperator:
   admissionWebhooks:
     enabled: false
+  tls:
+    enabled: false
   networkPolicy:
     enabled: true
 prometheus: