Add count of created jobs to ci_builds_total metric

See merge request !39

Pages usage is tracked by gitlab-pages now

See merge request !38

Update LICENSE year to 2017

See merge request !36

Closes #13

Update README.md

See merge request !33

Kudos to @yorickpeterse for the suggestion

Collect more DB tuple stats

Closes #12

See merge request !35

Closes #12

Track pages usage

See merge request !34

Update range to last 24 hours, not current day

See merge request !32

Add active runner count

Sometimes it is good to know how many runners are active. This way we could rule out if a large fleet was enabled.

The query takes about 33ms on GitLab.com, so can be safely added.

cc @pcarranza

See merge request !31

Split and refactor querying for total CI builds

This MR:
- splits metrics for builds in `running` state just like for the `pending` state (so projects are distinguished by`shared_runners_enabled` value),
- refactors querying for metrics about total builds count, so the data is collected with one query instead of two.

/fyi @ayufan

See merge request !30

This reverts commit 3c28bd41.

Add another CI Builds related metrics

This MR adds some CI Builds metrics:

- number of builds in `running` state, that were not updated since more than last hour,
- number of builds in `pending` state, that are created for projects with `shared_runner_enabled` set to `true`,
- number of builds in `pending` state, that are created for projects with `shared_runner_enabled` set to `false`,

```
ci_builds_stale{status="running",when="last_hour"} 2
ci_builds_total{status="pending",shared_runners_enabled_projects="1"} 5
ci_builds_total{status="pending",shared_runners_enabled_projects="0"} 2
```

MR is prepared on top of !27.

Related to gitlab-org/gitlab-ce#23366.

/cc @ayufan @ahmadsherif

See merge request !29

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

See merge request !27