fix(grafana): correct Prometheus datasource URL

Use prometheus-prometheus service instead of headless prometheus-operated service
for proper DNS resolution in Grafana datasource.

Author: batazor

ops/Helm/addons/observability/prometheus-operator/templates/grafana/datasources/prometheus-datasource.yaml

@@ -11,7 +11,7 @@ stringData:
       - name: Prometheus
         uid: prometheus
         type: prometheus
-        url: http://prometheus-operated.prometheus-operator:9090/prometheus
+        url: http://prometheus-prometheus.prometheus-operator.svc:9090
         access: proxy
         isDefault: true
         jsonData: