Encourage users to ask for missing extensions and to help implementing them

[ppalaga]

Originally proposed by @davsclaus on the chat:

I wonder if we should say somewhere in the docs that "if there is no Camel extension" then you can

1. create a ticket for it
2. help implement it (we love contributions)
3. it may still work with the camel component in jvm mode only (but an extension is a way to say its official supported, and to integrate better with quarkus)

Top of https://camel.apache.org/camel-quarkus/latest/list-of-camel-quarkus-extensions.html would be a good place for such a note