Allow passing arguments when using custom IP address supplier

When investigating x-site replication for one of more public clouds, we discover that it would be useful to have a Custom IP supplier that allows passing arguments into the supplier instance.

An example could look like the following: external_addr="custom:org.bla.Blah;args:LoadBalancerServiceName"

One might use the following demo for testing: https://github.com/infinispan-demos/JDG-x-site-replication-demo