Hi, sorry for the delayed response.
First of all, the Wikitech section you found is about the wikiprod Grafana instance at https://grafana.wikimedia.org. The WMCS Grafana instance (https://grafana.wmcloud.org) only queries data from various Prometheus instances, so for those we use Prometheus and prometheus-alertmanager directly instead of adding yet another component to the alerting stack.
So, yes, it is possible to configure e-mail or IRC alerts from the Prometheus metrics we collect from all Cloud VPS instances.[0] The bad news is that there's no self-service user interface for it yet, so you would need to ask a Cloud VPS admin to do any changes manually. It's not really documented anywhere yet, except this tiny section[1] which is aimed at admins who have direct access to the project.
I'm happy to do the changes if you have a Prometheus query to alert on written already, just create a task in the #Cloud-VPS project and tag me (@taavi) on it.
[0]: https://prometheus.wmcloud.org/ [1]: https://wikitech.wikimedia.org/wiki/Portal:Cloud_VPS/Admin/Monitoring#Monito...
Taavi