Corrected Configuration and avoid Conflict with Mediator.Outbox

Outbox was generally working, but would conflict with the Mediator.Outbox when it came to configuring. For now, replaced the method with a distinct call but ultimately one Outbox implementation should be possible, with Mediator/Kafka being just a minor implementation detail.

Key was a change made in the main code base that did not get carried through to this code-base, corrected that now so it should be functionally compatible with the latest changes made.