Update website dependencies

[zerok]

The website is currently built using a very old version of Gatsby. While none of the security issues that pop up should be exploitable as this is a static website, we should still update the dependencies in order not to run into a situation where maintaining it becomes impossible.

[Elfo404]

I briefly looked into this and the main packages used for the docs website seem all to be either very outdated or abandoned. the docz theme was dropped by its maintainer in favor of a new version that works on top of astro (see readme at https://github.com/doczjs/docz#readme), but that new version was never released.

Astro has a great package to make docs websites, https://starlight.astro.build/. I think it may be reasonable and sensible to move to it as it's more modern and has a lot more traction than gatsby.