Use a different metric name for new config CRUD APIs

Also, make sure to register the metrics with the same prometheus registerer
as the http server, so that metrics will show up.

pkg/api/http_server.go

@@ -387,7 +387,7 @@ func ProvideHTTPServer(opts ServerOptions, cfg *setting.Cfg, routeRegister routi
 			Namespace: "grafana",
 			Name:      "ds_config_handler_requests_duration_seconds",
 			Help:      "Duration of requests handled by datasource configuration handlers",
-		}, []string{"code_path", "handler"}),
+		}, []string{"handler"}),
 	}
 
 	promRegister.MustRegister(hs.htmlHandlerRequestsDuration)