Fix CI Runners Service dashbooard

In terms of visibility into length of the jobs queues, we have this chart:

src: https://dashboards.gitlab.net/d/000000159/ci?viewPanel=2&orgId=1&from=now-6h&to=now

However, it's inaccurate in two ways:

• it's outdated, because gitlab_exporter is pointed at the archive replica (which is lagging behind)
• it's incomplete, because most of the times the Postgres queries for pulling this data are timing out