Suggested re-working of Extensions authoring page

[nmcl]

With reference to https://quarkus.io/guides/extension-authors-guide

Lots of good information but perhaps too much information overload for someone wanting to write their first extension. Suggest the following modifications to the guide:

• is it possible to have a worked example running through the guide to help illustrate some/most/all of the concepts? Even if some basic example doesn't make sense, perhaps use one or more of the existing extensions? A worked example would be preferable though as developers can try it out as they read the guide and make their own modifications to the example to see what works and what breaks. Maybe even using the result as a template for their own first extension.

• split the guide into smaller linked pages taking the reader/potential author through the most common steps for writing a (basic/simple) extension. There's lot of information in the guide but how much of it is really needed by the first time author?

• perhaps link out to some extensions used in practice to get the author used to reading extension code in the context of the guide.

• split the guide into JVM and native sections. Some of the existing text refers to native-only actions on the part of the author so maybe these should be separate and only once someone has written a non-native extension.

[maxandersen]

duplicate/relates to quarkusio/quarkus#37288