Development branch testing dashboard

It would be super useful to have a dashboard that collects CI build statuses from packages that test against astropy dev (but only for those jobs). In many cases the failures are genuine downstream ones, but occasionally they may break as we did something unintended.

I'm not sure how to tackle this problem, but suspect that other big packages (numpy, matplotlib, etc.) may be interested such a tool, too to it may be a suitable hackday project to join efforts.

The issue does not name any files, tests, or entry points. Start by surveying how astropy and downstream packages configure CI jobs against the development branch, then define which jobs and statuses the dashboard would collect and what a useful result should display.

Written by the indexing model from the issue text.