added interface for rabbitmq eventbus

[tntwist]

Description

I have an use case where i need to customize the initialize-Logic of the RabbitMqEventBus.
For that reason i made the method "Initialize" virtual and added an interface for the RabbitMqEventBus, to use this interface over the implementation in the application initalization.

Checklist

• I fully tested it as developer / designer and created unit / integration tests - As no core logic is changed imho no testing is really needed.
• [ x ] I documented it (or no need to document or I will create a separate documentation issue) - Since no core logic is changed i guess there is no need for documentation.

How to test it?

Create a test app using rabbitmq as distributed event bus.