Support contextual context propagation

[FroMage]

Since a few releases already, SR-CP supports contextual context propagation, where you can affect the set of contexts that should be propagated in a given scope using the @WithThreadContext annotation on a method (via a CDI interceptor), or an equivalent API.

But in order to do that, you need to use the thread-local ThreadContext via SmallRyeThreadContext.getCurrentThreadContext() rather than create one yourself, in https://github.com/smallrye/smallrye-mutiny/tree/main/context-propagation/src/main/java/io/smallrye/mutiny/context

I can whip up a PR for that with some tests, probably next week if I don't forget.

[jponge]

That'd be great thanks @FroMage

[FroMage]

PR created.