fix: correct prom port

Author: RobHooper

salt/grafana/files/datasource.yaml

@@ -9,6 +9,6 @@ datasources:
       httpMethod: "POST"
       manageAlerts: false
     access: proxy
-    url: http://localhost:9090
+    url: http://localhost:9057
     isDefault: true
     editable: false