INT-3431: Fix `RecipientListRouter.onInit()`

JIRA: https://jira.spring.io/browse/INT-3431

The introduced `late channel resolution by name` via https://jira.spring.io/browse/INT-3324
has lost `onInit()` propagation from `RecipientListRouter.onInit()`
Well, again.
Somewhere I heard: 
> If your class hierarchy contains the third level, there is something wrong in your design

From other side, it looks consistent to have such levels of abstraction to follow with domain.
My idea is: since we must initialize the `super` independently of its implementors, we should have some hook to allow to do that without affect of `super`: it is really a bad design, when a child corrupts his parent.

Groovy's `FactoryBuilderSupport` provides a hook to invoke methods from its implementors with `register` prefix on initialization phase. I find it as very convenient feature.

As long as Java isn't so friendly we can provide only workaround like `InitCallback` and have a stack of them in parent, to iterate and call each of them. The method `addInitCallback` should does the stuff from any children level without affect of `super`.

Otherwise we should live with this bottleneck andjust go ahead with test coverage on the matter and with more useful feature.

WDYT?