Add support for Reactor thread locals propagation

[nathankooij]

Current module is not sufficient for Reactor because it does not provide support for decorating Callables which are used by Reactor's schedulers. Moreover, we can leverage Reactor's subscriber context mechanism to ensure propagation whenever Reactor's schedulers are not used (e.g. Netty and the Reactive Mongo driver use their own event-driven scheduling mechanism).

[bsideup]

not sufficient for Reactor because it does not provide support for decorating Callables which are used by Reactor's schedulers

FYI starting from Reactor 3.3, there is Schedulers.onScheduleHook() to do so. And, before 3.3, there was Schedulers.addExecutorServiceDecorator() for it.

Although I agree that using Reactor's Context is the best way to achieve it 👍