Deploy Prometheus Rules and Alertmanager from gitlab-helmfiles instead of runbooks

Ideally the runbooks pipelines shouldn't be deploying anything directly to our GKE clusters, it's a security concern and we are also ending up with the Prometheus configuration being deployed from 2 projects at the same time (runbooks and gitlab-helmfiles).

An alternative would be to generate the Prometheus Rules and Alertmanager configuration from the runbooks pipeline and publish them as CI pipeline artifacts. Then the gitlab-helmfiles pipeline can fetch those artifacts and deploy them as part of the Prometheus release.