Add basic metrics for CI Builds
This MR adds basic metrics for CI Builds. Currently there is a support for:
- number of all builds (works for CE and EE)
- number of builds executed per runner (works for CE and EE)
- number of builds executed per runner for mirrored projects (works for EE, returns
0
on CE)
Output looks like:
ci_builds_total{status="running"} 0
ci_builds_per_runner{status="running",runner="8",mirrors="0"} 0
ci_builds_per_runner{status="running",runner="8",mirrors="1"} 0
ci_builds_per_runner{status="running",runner="9",mirrors="0"} 0
ci_builds_per_runner{status="running",runner="9",mirrors="1"} 0
References gitlab-org/gitlab-ce#23366
/cc @ayufan