Currently we geneate our docs using a build script at
https://github.com/tigerbeetle/docs and content from
https://github.com/tigerbeetle/tigerbeetle.

Streamline this by moving the content and build script together.

Note that I regenrated lockfile from strach during the import, to shrink
its size from 1.5MiB to 0.7MiB, and to fix couple of issues reported by
`npm audit`.

- remove docker: I believe it's docusaurus job to come up with correct
  hashes for the content, independent of the build machine.
- remove repo cloning dance --- that's the purpose of this PR, no need
  to clone anything if everything is in the same repository
- remove the old hack --- condition on the link rewriting

Our sed link rewriting produces a garbage URL here.

No need to copy between docs & build, as we'll be preparing the repo
manually anyway.

`./zig/zig build ci -- langauge=node` now does the equivalent