Support installation from tarball

[Kha]

In contrast to the install script, tarballs can be sourced directly from Hydra: https://github.com/leanprover/lean4/blob/e8b58abffcf2eadc436435cf6e6733827d818ed6/.github/workflows/nix-ci.yml#L34-L44

[Kha]

(The singler-user installation workaround I'm doing there doesn't seem to work well and it looks like it might be removed from the macOS setup soon anyway, so I'd be glad to switch back to using install-nix-action directly when this issue is solved)

[domenkozar]

@Kha what problem are you trying to solve, it's not clear to me :)

[Kha]

The goal was to install arbitrary Nix master versions, so I suppose this will be covered by NixOS/nix#4549. Just for the record, the main advantage of using tarballs directly is that the only dependency is Nix Hydra, but with the downside that you have to find the correct URL per platform.

[domenkozar]

I'm fine adding tarball support if someone wants to take a try :)