[Doc] Bootstrap headless documentation

[djhi]

Bootstrap headless documentation with Astro Starlight

How To Test

• make doc-headless
• Click the Get started button
• Resize your window to be very small. In a new tab, enter http://localhost:4321/ra-core/reference/example/: note the sidenav scroll is sync

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.

[slax57]

Otherwise it indeed allows to get a really nice doc website with very few code, I love it!