According to some rework and deprecations in the latest Reactor,
fix Reactor-based components to follow with the latest paradigmas
* Use `Flux` wrapper in the `ReactiveChannel` to track cancellation
instead of deprecated `Operators.SubscriberAdapter`
* Do similar `Flux.from(publisher)` in the `doSubscribeTo()`
to avoid subscribers delegation and, therefore, unnecessary call stack
* Rework `ReactiveConsumer` to wrap to a new `BaseSubscriber`
on each `ReactiveConsumer.start()`.
We need this wrapping to prevent subscriber cancellation from the
upstream `Publisher` on error.
We can't rely here on the `Flux.retry()` because upstream
`DirectProcessor` is marked as terminated on any error
Apply Reactor-3.0.6.RELEASE
499e1167d1