Description of problem:

When UWM Alertmanager is enabled and the Ruler tries to send an alert to UWM Alertmanager it get's denied with 403.

I enabled high verbose logging on kube-rbac-proxy in the UWM Alertmanager pod and I saw that the Ruler is failing the SAR with:

alertmanager-proxy I0108 20:37:25.898884       1 request.go:1172] Response Body: {"kind":"SubjectAccessReview","apiVersion":"authorization.k8s.io/v1","metadata":{"creationTimestamp":null,"managedFields":[{"manager":"kube-rbac-proxy","operation":"Update","apiVersion":"authorization.k8s.io/v1","time":"2024-01-08T │
│ 20:37:25Z","fieldsType":"FieldsV1","fieldsV1":{"f:spec":{"f:extra":{".":{},"f:authentication.kubernetes.io/pod-name":{},"f:authentication.kubernetes.io/pod-uid":{}},"f:groups":{},"f:resourceAttributes":{".":{},"f:group":{},"f:name":{},"f:namespace":{},"f:resource":{},"f:subresource":{},"f:verb":{}},"f:uid":{}," │
│ f:user":{}}}}]},"spec":{"resourceAttributes":

,"user":"system:serviceaccount:openshift-logging:lokistack-dev-ruler","groups":["system:serviceacco │
│ unts","system:serviceaccounts:openshift-logging","system:authenticated"],"extra":{"authentication.kubernetes.io/pod-name":["lokistack-dev-ruler-0"],"authentication.kubernetes.io/pod-uid":["91023287-38c1-4465-bd1d-423ed1692e08"]},"uid":"ad1745bc-1661-4f24-a776-26d0e16d986e"},"status":{"allowed":false}}           │
│ alertmanager-proxy I0108 20:37:25.898983       1 auth.go:97] Forbidden (user=system:serviceaccount:openshift-logging:lokistack-dev-ruler, verb=create, resource=alertmanagers, subresource=api). Reason: "". 

Version-Release number of selected component (if applicable): 4.15.0-rc.1

How reproducible: Always

Steps to Reproduce:

1. Provision 4.15.0-rc.1
2. Enable UWM Alertmanager
3. Create a User Logging Alert
4. Check the Ruler logs for 403 errors

Actual results: Ruler gets 403 when sending Alerts

Expected results: Ruler should not get 403

Additional info: