Improve handling of host, port, and addresses configuration in RabbitProperties

[philwebb]

#18808 will add support for amqps:// support but we have isEnabled and getPort methods that change depending on the address. Changing those to Object types and making them null might help us fix them.

[snicoll]

There are more features that are potentially misleading at the moment. To make things consistent, we've considered revisiting the description of such properties to mention that specifying an address takes precedence.

As for the port it should be Integer in any case as it has two "default" values.

[wilkinsona]

Let's look at this for 2.3.0.M2.