Bundling Prometheus For GitLab CE

Continued from #1008 (closed)

Customers tend to not have monitoring set up. If we ship it with GitLab this situation will improve. We can also use this monitoring for the applications GitLab deploys. What users are looking for is simple experience similar to the of New Relic (a few clicks and you're up), for that we need to create:

1. Easy plugins for popular frameworks
2. An instant dashboard

This is reflected in: https://gitlab.com/gitlab-org/gitlab-ce/issues/23841

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This issue focuses only on monitoring the GitLab instance and presenting the metrics on a dashboard.