Create ghcup meta information file
Purpose of meta information file:
- detect new GHC and cabal-install versions on-the-fly without requiring users to update the script in-place
- download reliability: meta information may contain download url information in addition to versions
Questions to answer:
- where should this file be hosted? (downloads.haskell.org or this repo?)
- which format? (should be easily parsable/sourcable by shell/awk or do we want to go for json/toml and use dependencies for parsing)
- consider that the format might be extended in the future
- what information should it hold exactly?
- available ghc/cabal-install versions?
- latest ghc/cabal-install version?
- "good" or "bad" versions (e.g. known buggy releases) and reason
- what is the method/process for updating this meta information file?