publish docs to /docs/main

[rukai]

This PR implements just the doc generation for main branch portion of #1853

This PR introduces the website crate for generating the shotover website, which currently just:

• generates the mdbook for main branch at docs/main
• allows serving the website when --serve is passed.
  It also adds the publish-to-pages github actions workflow responsible for running the website crate and uploading the result to the github pages for this repo.

Refer to #1853 for the full analysis.

[codspeed-hq]

CodSpeed Performance Report

Merging #1854 will not alter performance

_{Comparing rukai:publish-pages-poc (21dddb4) with main (b846d2e)}

Summary

✅ 38 untouched benchmarks