[Alerting]: Assign UUID to grafana receivers (#34241)

* [Alerting]: Assign UUID to grafana receivers

* Apply suggestions from code review

* Add test for updating invalid receiver

Co-authored-by: Domas <domasx2@gmail.com>

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -67,8 +67,9 @@ func TestNotificationChannels(t *testing.T) {
 		alertsURL := fmt.Sprintf("http://grafana:password@%s/api/alertmanager/grafana/config/api/v1/alerts", grafanaListedAddr)
 		resp := getRequest(t, alertsURL, http.StatusOK) // nolint
 		b := getBody(t, resp.Body)
+		re := regexp.MustCompile(`"uid":"([\w|-]*)"`)
 		e := getExpAlertmanagerConfigFromAPI(mockChannel.server.Addr)
-		require.JSONEq(t, e, b)
+		require.JSONEq(t, e, string(re.ReplaceAll([]byte(b), []byte(`"uid":""`))))
 	}
 
 	{