docs(turbopack): build more docs

[kwonoj]

What

This PR changes setup for the turbopack documentation.

Long story in short, we want to 2 types of documentation: one for high level description (archtecture, etcs) and another for the api doc. rustdoc / cargo doc unfortunately doesn't support to integrate both easily.

PR adds mdbook setup to workaround those - instead of using rustdoc's index as entrypoint, mdbook becomes an entrypoint to rustdoc. This allows to host plain text document, and also able to access full rustdoc pages.

preview: https://turbopack-rust-docs-b6qta4xdq.vercel.sh/
rustdoc: https://turbopack-rust-docs-b6qta4xdq.vercel.sh/rustdoc/index.html

Closes PACK-2475
Closes PACK-2468

[ijjk]

Stats from current PR

Default Build

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buildDurationCached	6.6s	5.1s	N/A
nodeModulesSize	196 MB	196 MB	✓
nextStartRea..uration (ms)	412ms	405ms	N/A

Client Bundles (main, webpack)

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Legacy Client Bundles (polyfills)

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Rendered Page Sizes

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Edge SSR bundle Size

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Middleware size

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pages.runtim..prod.js gzip	22.1 kB	22.1 kB	✓
server.runti..prod.js gzip	49.9 kB	49.9 kB	✓
Overall change	925 kB	925 kB	✓

Commit: 1b73f1c

[ijjk]

Tests Passed