[API] Add GET /api/v1/status.
[Migration] Update initial migration with a few GH specific fields.
[Gemfile] Add github_api.
[Pod] Add .without_github_metrics and .with_old_github_metrics.
[Metrics] Rename to PodMetrics.
[Metrics] Ditto.
[Github] Add Metrics::Github and Metrics::Updater.
[Rackup] Load and run Metrics::Updater.