Fixes: #8981
Sometime the simple `boolean failover` on the `MessageChannel` (default `true`)
is not enough to be sure that we can dispatch to the next handler or not.
Such a decision can be made using `ErrorMessageExceptionTypeRouter`, but that would
require an overhaul for the whole integration flow
* Introduce a simple `Predicate<Exception> failoverStrategy` into `UnicastingDispatcher`
and all its `MessageChannel` implementation consumers to allow to make a decision about next failover
according to a thrown exception from the current `MessageHandler`
* Expose `failoverStrategy` on the `DirectChannel`, `ExecutorChannel` & `PartitionedChannel`,
and add it into respective Java DSL specs
* Fix involved tests to rely on the `failoverStrategy` property from now on
* Document the new feature
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