[Windows] Integrate better with msys2 and cabal config

[hasufell]

The current windows images don't have a cabal config, so everything is default. haskell/actions sets the store-dir, but nothing else. That means, in order to be able to use msys2 packages, a user would have to set:

• extra-prog-path
• extra-include-dirs
• extra-lib-dirs

And figure out where the pre-installed msys2 is, etc. etc.

This is cumbersome. I've suggested to add this config to the windows images here actions/runner-images#4264 but it's debatable. If we decide to not do this, then the haskell action should have easier means to:

1. set all of the above cabal config values to the right thing (maybe via a boolean config option or unconditionally)
2. allow installation of additional msys2 packages in the pre-installed msys2 instance

[hazelweakly]

I already have to modify the windows cabal config to set the store-dir so I'm very open to adding the extra-* dirs required to get msys2 working correctly. I checked the PR and don't actually see where the cabal config is getting modified; is the cabal file getting modified in that PR or are you suggesting we modify the cabal config in haskell/actions?

The src/setup-haskell.ts file is where the cabal file currently gets modified. I'm happy to add any additional modifications that make using haskell on github actions a smoother process