Switch to Docusaurus

[askvortsov1]

I think we should consider switching to Docusaurus instead of VuePress for our docs system. A few advantages:

• Designed to work with crowdin, which we want to use
• Has a scalable way to manage multiple types of docs for extend, admin, user, core dev, etc. We'll want to add more of these, so this flexibility is handy.
• Much less config needed for internationalization
• Dark mode!
• Built-in ToC
• Powered by React, which is pretty cool!
• Supports a landing page, as well as blog/static pages if we wanted that
• Has great versioning support for when we move to v2

[tankerkiller125]

I'm going to close this as we have in fact switched to Docusaurus successfully and have been using it for several months now.