Implement monitoring for self-hosted GHA runners #11
Description
It would be nice to implement monitoring for self-hosted runners, to ensure all of them are online and see how many are busy at any point in time. API documentation.
monitorbot_gha_runner_online{repo="rust-lang-ci/rust", runner="arm-1-1"} 1
monitorbot_gha_runner_busy{repo="rust-lang-ci/rust", runner="arm-1-1"} 0
This will need a "general" environment variable to configure the GitHub API token used by monitorbot for its API calls, and a variable to list the repos to monitor for self-hosted runners.