GitLab.com latency monitoring page

Part of https://gitlab.com/gitlab-com/infrastructure/issues/947

Needs federated monitoring https://gitlab.com/gitlab-com/infrastructure/issues/760

The idea is to have one public dashboard to show why GitLab.com is slow, it needs to have:

1. Latency of 99% th percentile of requests (OKR goal)
2. Number of user sessions
3. Number of unicorn processes
4. CI builds
5. Transaction timings
6. HTTP Queue timings
7. Things that are now on http://monitor.gitlab.net/dashboard/db/gitlab-status