Add GitLab metrics to metric library
Problem to solve
Currently metrics for a GitLab server have to be manually added via custom metrics, which is time consuming and requires manual effort.
We should add the GitLab metrics to the metrics library, so they are detected automatically. We can largely base the metrics and charts on the standardized metrics we already have in the existing Grafana dashboard we publish: https://gitlab.com/gitlab-org/grafana-dashboards
We will need to curate the grafana dashboard, as it currently occupies 3 dashboards and we only currently support one at a time.
What does success look like, and how can we measure that?
We can measure how many times the GitLab metrics are detected, and report that in the usage ping.