Refurbish the documentation

[chandryan]

Description

The documentation is currently in a single file in docbook format. It would be nice to have it in a more "edit-friendly" format and structured across multiple files.

Goals:

• Migrate the documentation to AsciiDoc & Antora
• Provide a PDF export
• Generate a (doxygen, MrDocs?) API documentation
• Detect broken anchors automatically (https://docs.quarkiverse.io/quarkus-antora/dev/testing.html)