prometheus: fix prometheus target url

The prometheus service isn't binding on localhost.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1933560

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 1d568186)

roles/ceph-prometheus/templates/prometheus.yml.j2

@@ -8,7 +8,7 @@ rule_files:
 scrape_configs:
   - job_name: 'prometheus'
     static_configs:
-      - targets: ['localhost:{{ prometheus_port }}']
+      - targets: ['{{ grafana_server_addr }}:{{ prometheus_port }}']
   - job_name: 'ceph'
     honor_labels: true
     static_configs: