Expose metrics

[stigok]

It would be helpful to expose some metrics for the app's internals.
Especially how many GitHub API requests we have made, so we can keep track of how far away we are from the hourly rate limits.

[stigok]

Live GitHub rate limit status can be found here https://docs.github.com/en/rest/rate-limit/rate-limit?apiVersion=2022-11-28#get-rate-limit-status-for-the-authenticated-user