Provide an abstractions package

### Describe the feature request
I want to be able to have a library which handles amqp messages without needing to take on a dependency of the entire amqp library which includes a client etc.

### Describe the solution you'd like
I am looking at optimising the cloud events SDK which provides a binding for AMQP but currently the entire library is needing to be taken on as a dependency which is not really necessary given the limited functionality scope. As such I would propose releasing an abstraction package which provides at a minimum the classes for handling the message and that is a dependency of the client.