Add download page simplification proposal

[hasufell]

Rendered version: https://github.com/hasufell/committee/blob/proposal-0004/proposals/0004-download-page-simplification.md

[tomjaguarpaw]

Similarly to my haskell-infra/www.haskell.org#93 (comment), to make progress with this we need buy in from a wide variety of stakeholders, including representatives from at least Stack and Chocolately. cabal and GHC would be helpful too.

[hasufell]

Right... I think a few things to consider are:

1. what's the right location for a user-editable wiki page of alternative installation instructions? Maybe it should live at GHC wiki?
2. I haven't heard back from stack team about my GHC installation hook proposal yet: Support custom GHC installation hooks commercialhaskell/stack#5585 ...this would solve the "duplicate GHC install" problem and allow many more integrations (e.g. using package manager provided versions, nix, other installers etc.)
3. communicate clearly that ghcup is not a replacement for stack and doesn't intend to be ever

[hasufell]

I'm withdrawing this proposal for now, until we have a better picture about what the different stakeholders of the tooling landscape want. Pushing the discussion via a proposal seems to have failed, so I hope we can have better discussions in the future.