Fix serverName to include namePrefix applied by Kustomize

Kustomize does not automatically replace string values in serverName field.
Additionally, Kustomize applies namePrefix to Service names.

Service name in config: metrics
After Kustomize namePrefix: openstack-lightspeed-operator-metrics
DNS name: openstack-lightspeed-operator-metrics.openstack-lightspeed-operator-system.svc

Changed from: metrics.system.svc (incorrect placeholder)
Changed to: openstack-lightspeed-operator-metrics.openstack-lightspeed-operator-system.svc

This ensures TLS verification will succeed when Prometheus validates
the certificate's SAN against the serverName.

Fixes issue raised by omkarjoshi0304 in PR review.

Author: malingatembo

config/prometheus/monitor.yaml

@@ -16,7 +16,7 @@ spec:
       bearerTokenFile: /var/run/secrets/kubernetes.io/serviceaccount/token
       tlsConfig:
         caFile: /etc/prometheus/configmaps/serving-certs-ca-bundle/service-ca.crt
-        serverName: metrics.system.svc
+        serverName: openstack-lightspeed-operator-metrics.openstack-lightspeed-operator-system.svc
   selector:
     matchLabels:
       control-plane: controller-manager