Provide an overloaded JmxConfigurator.registerChannel that takes an ObjectName to be used as prefix instead of the domain

The JmxConfigurator.registerChannel variant that takes a domain is not enough for use cases where multiple apps running in a jvm join the same JGroups cluster and also share the same jmx domain. In this case the channel MBean object names will collide. The de-duplication mechanism using random number suffixes does not provide predictable results. Avoiding jmx domain sharing is also not possible due to the nature of the use case.

So we propose adding someting like this:
JmxConfigurator.registerChannel(JChannel channel, MBeanServer server, ObjectName namePrefix, String cluster_name, boolean register_protocols)

which would allow the application using JGroups to have greater control of the generated object names for channel and protocols. The namePrefix will provide the domain and also a key-value list that will serve as the prefix for all ObjectNames internally generated by JGroups. It will be the caller's task to ensure this leads to generation of unique names.