Ensure the alert rules are deployed again from the nix code

Since #159 (closed), I've noticed we have only 4 alerting rules for HRO Cloud:

While we have 16 more on staging and production (20 rules thus):

I suppose we should have more or less the same rules everywhere!?

Maybe we could re-use the file provisioning we have in place for the contactPoints.

https://grafana.com/docs/grafana/latest/alerting/set-up/provision-alerting-resources/file-provisioning/#import-alert-rules