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()`
It seems to me, that it is a bad design: if this object before usage should be initialized, it is required to invoke its `afterPropertiesSet()` first of all.
I guess that it is here, because our tests aren't consistent, and it is easier to do initialization here, rather than fix all non-contaier tests.
BTW all other our components don't do the same from critical points and we just rely on Spring Container.
So, I won't mind o change it to `afterPropertiesSet()`, as far as it won't hurt, because in real apps this component is always a bean.