[Discussion] Install ghcup (optionally, on user request) via extension?

Currently we don't and refer the user to the ghcup download homepage, because:

1. it forces them to get a basic understanding of what ghcup is and how they can use it outside of VSCode
2. it requires them to set up PATH properly and understand how to run `ghc`/`ghci` outside of VSCode
3. on windows, it also installs msys2 on demand (or lets them point to an existing msys2), sets up cabal config and environment variables
* ghcup itself currently cannot install msys2, only the powershell bootstrap script

@wz1000 suggested that the extension may install ghcup. The main challenges here are:

1. how to deal with msys2 on windows
2. can we run the *interactive* bootstrap scripts on both linux and windows through the extension?