'ghcup satisfy' command

This command could install the correct GHC version in a cabal project based on various metrics:

1. look for a stack.yaml and pull the GHC version from the resolver/config
2. look for cabal.project for pinned compiler
3. interpret foo.cabal and figure out the maximum base constraint (how?) and then use a base-ghc mapping to install the correct GHC

Third option seems like the gold standard, but in order to find the highest allowed base version, we need to do an actual resolution I believe...

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Edit: plan.json we cannot use, because that requires a cabal run with ghc already installed I believe.