Extend binary installer to support the new /stable endpoint

[Leonidas-from-XIV]

This PR extends the binary install script with support for querying the /stable endpoint and extends the website to mention it. I thought it would be neat if the website mentioned the latest release so this is exactly what it does now.

I took the sh -s trick from dune-bin-install, however I am unsure how the call should look like. The way sh -s works is it sets argv, even including argv[0]. This means that we always have to pass some argument to sh -s to fill argv[0] before filling the rest of argv.

In the current state of this PR I just tell people to pass - as it doesn't really matter what argv[0] is, but arguably that's a bit ugly. dune-bin-install handles it by pretending argv[0] is a proper argument (instead of just the executable name) and parses the version information out of it, which allows it to avoid one argument to sh -s.

As I see it there are multiple ways of handling this:

1. Keep it as is, require sh -s <RANDOM> <ACTUAL_ARGS> (this PR currently sets <RANDOM> to -)
2. Copy dune-bin-install and interpret argv[0] as version (| sh -s 3.21.1)
3. Do some switcheroo and start parsing command line arguments from argv[0] ($0 in shell) instead of the usual argv[1] ($1), that way we could do | sh -s --release 3.21.1

The latter two are a bit wonky because if someone downloads the script and then calls it (with ./install or so) then argv[0] will be set to ./install (or so), thus we have to handle the cases of "launch from shell" and "pipe into sh" quite differently.

Your insights and ideas are greatly appreciated.

[Alizter]

Did you run the server locally and test the script?

[Leonidas-from-XIV]

Yes, I ran the server and it displays the new line with the right stable version. I've also tested installation of stable and nightly versions on an alpine:3.23 container (both work).

[Leonidas-from-XIV]

@Alizter Do you have any opinion on the sh -s behavior? Should we keep it at | sh -s - --release 3.19.0?

[Alizter]

I think - is best. We don't want to be too creative or cause surprises. We should make sure this command is copy-pastable from the website for the release versions anyway.

[Leonidas-from-XIV]

I think - is best. We don't want to be too creative or cause surprises.

Perfect! In fact it could be anything else as well (e.g. --), it just needs to be there fill up argv[0].

We should make sure this command is copy-pastable from the website for the release versions anyway.

Yes, that's part of this PR. In lib/main.mlx I am generating the command to install a stable release.