Integrate the use of ghcup to download the required toolchain

[jneira]

Moved from haskell/haskell-language-server#2251

• Depending on the info given by hls-wrapper:
  • cabal cradle: do a ghcup install cabal && ghcup install ghc ${version}, where ${version} will be the ghc version reported by the cradle or empty if it is not known, after downloading cabal itself (needed for query the ghc version)
    • it will download only the missing tool, cabal or ghc
  • stack cradle: do a ghcup install stack and let stack download the rest of needed tools (as with the default stack via ghcup will download ghc and/or msys2 in its own)
  • direct cradle: do a ghcup install ghc
  • bios cradle: do nothing
• We have to decide what to do if ghcup itself is missing:
  • do nothing
  • download ghcup
  • suggest user install it
• The automatic download will be configured and maybe we should do a one-off question to let users decide the default behaviour