Add Stack aarch64 binaries

It'd be nice if we could install stack on aarch64 using ghcup. I'm currently trying to build stack from source on an RPi4 and it's taking forever. I'd love to be able to save others from this pain in the future. Where are the binaries used by ghcup kept? How should I submit my artifact when I'm done?

I have binaries, but I'm not comfortable with distributing my own stack binaries. Stack should add aarch64 support.

For unofficial binaries check out: https://downloads.haskell.org/~ghcup/unofficial-bindists/stack/2.7.3.1/

added scopeupstream label

Upstream report: https://github.com/commercialhaskell/stack/issues/5619