docs: migration to Astro

[julien-deramond]

This PR migrates our documentation to Astro based on previous work at #38319.

🌟 Netlify preview

Sub-tasks

• Fix Netlify deployment
• Gather all documentation-related commits from 1fe9067; the previous PR stopped around March 2023 so I started to gather commits from begining of March 2023.
  • Last commit gathered: 163f1f7 (continue from https://github.com/twbs/bootstrap/commits/main/?before=90acd33350e1356194a364595cb07b65f24bd611+105)
• Double-check the content of what comes from site/assets (must be the latest versions at the end)
• Bump Astro dependencies (see c49f234)
  • Double-check the impact of this migration. For instance, there's at least a regression with this commit ->

becomes

• Migrate to modern way of handling Astro websites (check migration guides)
• Re-enable progressively .github/workflows/*
• Move from site-new to site
  • Astro shouldn't use site/data/docs-versions.yml
• Change scripts names to use old ones OR migrate the entire documentation to build and deploy the website
• Delete all Hugo references
• The documentation generated/built must work within the gh-pages with the same process as before at first
• Check /docsref page
• Check Placeholder component precisely (see for instance f52d4a3)
• Check duplicates between ./site-new/public/docs/5.3/assets/img/examples/*.png and ./site-new/static/docs/[version]/assets/img/examples/*.png
• Handle this change precisely: f8a56da
• For all <ScssDocs where file="site" -> find the site-new reference so that npm run astro-build builds correctly
• Double-check the rendering of all pages
  • Special check for the migration page (including the diff rendering)
• Check more in detail 1729bcc compared to the new Code.astro file
• Double-check the rendering of <JsDocs> from 06f7c3b + 34c2725 + e2854b9 (compared to main branch)
• Double-check 74c6f2b has been correctly reintegrated
• Check if there's anything to do with e468daa#diff-90090845e271c47d4fb564334a22156612e18b9bbc61397ed6dcc29bb6ddb20a (site/layouts/_default/examples.html with integrity values etc.)
• /docs/5.3/examples/dashboard-rtl/ and /docs/5.3/examples/dashboard-rtl might give different results (load or won't load the CSS + JS)
• Check for duplicate images/paths like ./site-new/public/docs/5.3/assets/img/guides/parcel-dev-server.png versus ./site-new/static/docs/[version]/assets/img/guides/parcel-dev-server.png
• Check 688d7e3 so that we maybe add the aria-label if not present by default in Astro
• In index.astro examples, double-check that the external scripts and links have been set with the latest version + integrity
• Fix Stackblitz JavaScript part (file integrated into Stackblitz but doesn't do anything)
• We didn't use defer (see 45fe28c); do we need that with Astro?
• Handle correctly the sitemap (see 9480a3d + 72d3b6e)
• Render image hook? (see 2ba7dae#diff-14181aac55c6feb7b2a6e08c61d78e3f31be6f31b6e206a365cdcc3e9d0b5934)
• Check all TODO(Astro migration) comments

[julien-deramond]

&& rm -rf _site && cp -r site-new/dist _site is temporary to make Netlify works as it checks the built content in _site