Meta: use vitepress for docs

[KaelWD]

The current documentation site is annoying to use as it has no global navigation links and performs a full refresh on page change. This PR renders the docs with vitepress which comes with SPA navigation, a dark theme, searching, and a sidebar with links to every other page instead of having to go back through the index.

[Ms2ger]

Hi! Could you give a bit more background on what the goal of this PR is?

[KaelWD]

I've added a PR description. This was initially for my own use because I was frustrated with the current site and there doesn't seem to be any progress on #1449 yet.

[ptomato]

I'm hesitant about this because I'm not familiar with Vitepress and would not be able to debug it. But on the other hand, it does solve an actual problem: the lack of navigation sidebar is annoying in the current docs and has been for a long time.

Does Vitepress have any mode where it can just generate the site with all the assets in place such that they can be loaded with relative paths, as the current site does? Not having to spin up a HTTP server with vitepress dev when developing the docs locally would solve one of my hesitations.

[KaelWD]

That doesn't seem to be supported unfortunately: vuejs/vitepress#3057

[ptomato]

@KaelWD Thanks for contributing this. We discussed it in the Temporal meeting today and unfortunately decided not to merge it. Basically we see it as somewhat of a risk to change the docs framework at this point. However it's clear there is a need for better navigation features, especially a sidebar, and so a few of us volunteered to look into implementing a sidebar in the current static website.