Index configuration properties and provide a dedicated search endpoint (and webapp?)

[yrodiere]

The full list of (core) configuration properties on the Quarkus website is huge. Search is also implemented in Javascript, and performance has become quite bad -- at least in my case, testing with Firefox.

We should consider having a dedicated index for configuration properties on search.quarkus.io, so that this page's search feature could be offloaded to search.quarkus.io, similarly to what we did for https://quarkus.io/guides

How to perform indexing exactly is TBD:

• We could scrape the full HTML page, though that would be potentially fragile and prevent us from collecting interesting metadata (e.g. source extension).
• We could use extension metadata directly, though it would be more complex to retrieve (where is that metadata?) and may involve Asciidoc rendering.
• ... something else?

cc @gsmet: your overhaul of config annotation processing and metadata (quarkusio/quarkus#42141) will most likely have an impact here.