changelog: add notes about closing #11555

[skip ci]

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### Minor
 
 * **Alerting**: Link to view full size image in Microsoft Teams alert notifier [#13121](https://github.com/grafana/grafana/issues/13121), thx [@holiiveira](https://github.com/holiiveira)
+* **Postgres/MySQL/MSSQL**: Add support for replacing $__interval and  $__interval_ms in alert queries [#11555](https://github.com/grafana/grafana/issues/11555), thx [@svenklemm](https://github.com/svenklemm)
 
 # 5.3.0-beta1 (2018-09-06)