Add prometheus cluster application (!47) · Merge requests · GitLab.org / cluster-integration / Cluster applications

Based on prometheus GMA implementation

This implementation is not fully functional, some things are not possible to do at the moment:

Prometheus service has to be activated post install: https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/models/clusters/applications/prometheus.rb#L20-33 . We also need to handle removal.
Prometheus service is not exposed on the external address, we instead rely on the k8s proxy url that has to be propagated back to gitlab: https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/models/clusters/applications/prometheus.rb#L88

gitlab-org/gitlab#202002 (closed) should potentially introduce a way to achieve this.

Add prometheus cluster application