Rethink extension build time instantiation of DefaultCamelContext

There's a few places outside of the CQ core where extensions explicitly instantiate their own `DefaultCamelContext` so that they can use it to pre-load stuff or get access to Camel resources in order to do build time enhancements.

This feels a bit heavyweight and has some limitations:

* It slows down the build time code. Especially if you have all extensions that create `DefaultCamelContext` on the classpath.

* It spams the build time logs with `CamelContext` messages which is potentially confusing for folks.

* Occasionally we need to do special patches to fix issues (see #6642). The service discovery mechanism we have for `FastCamelContext` does not apply to `DefaultCamelContext`. So we loose the ability to easily exclude / include services etc.

Maybe there's a more lightweight way to do things or have 'just enough' `CamelConext` to fulfil whatever build time requirements these extensions have.

Start by locating extensions that explicitly instantiate DefaultCamelContext for build-time preloading or resource access. Review the FastCamelContext service-discovery mechanism and the special handling described in #6642. Done means build-time extensions have a lighter suitable context, avoid unnecessary CamelContext log messages, and retain the needed enhancement behavior.

Written by the indexing model from the issue text.