Tooling to run head.hackage against all of stackage nightly

I think it would be nice if we had the capacity to run head.hackage against the latest stackage nightly to see how much breakage we have in store. It would be especially nice if it could give us a nice breakdown of why things didn't compile, eg, if a single package is blocking large parts of the ecosystem.

If this sounds alright, I'll give a go at implementing it in when I have some time. I think this would be nice as an optional job/pipeline.