Migrate docs to Docusaurus v3

[clemyan]

What's the problem this PR addresses?

The docs website is on Docsaurus v2 which is not the latest major version

Closes #5918

How did you fix it?

Migrate to Docsaurus v3.

There are other improvements to the build process and website I'd like to make, but I have left them out and kept most of the logic intact since the migration is quite a large undertaking already.

Checklist

• [x] I have read the Contributing Guide.

• [x] I have set the packages that need to be released for my changes to be effective.

• [x] I will check that all automated PR checks pass before the PR gets reviewed.

[clemyan]

Turns out, the package info page uses some of docusaurus's internal components and is broken after the migration. Marking the PR as draft for now.