gitlab monitoring

we need to have gitlab metrics in grafana. we also need to make sure things work (nagios).

this implies monitoring the webserver (nginx i guess?) and it would also be nice to have internal gitlab metrics. there's a builtin prometheus exporter in gitlab so we should be able to reuse that. see:

https://docs.gitlab.com/ee/administration/monitoring/prometheus/ https://docs.gitlab.com/ee/administration/monitoring/prometheus/gitlab_metrics.html