Port JGroups to Quarkus [1].

This is a quick and dirty port, to see what needs to be done.

The goal is to identify changes which can be ported back to JGroups proper to make this port as easy as possible.

Example: since JMX is not supported, separate JMX into a set of interfaces and 2 implementations: the default impl which is used when JGroups runs on a regular JVM, and another one used when run on GraalVM.

This is currently scheduled for 4.x, but may as well end up being done in 5.x

[1] https://quarkus.io