outbound-socket-binding element should allow grouping which subsystems can reference

Useful especially for clustering subsystems like jgroups discovery protocols, infinispan hotrod servers, and mod_cluster balancers.

JGroups configuration can use two different ways to configure cluster detection

------ older configuration is via protocol properties –
<protocol type="TCPPING">
<property name="initial_hosts">host[7600]</property>

------ new configuration via socket reference
<socket-discovery-protocol type="TCPPING" socket-bindings="ref-a ref-b"/>
...
<outbound-socket-binding name="ref-a">
<remote-destination host="127.0.0.1" port="7600"/>
</outbound-socket-binding>
-----------

with the old option it is possible to use an expression to set all hosts in a cluster.
The new one need to have all outbound connections listed which is harder to maintain.

As an administrator I want to have the possibility to group the connections and only have one reference and the number of connections can be vary without changing multiple point in the configuration.
So a configuration like this would enhance that

    <outbound-socket-binding-group>
        <outbound-socket-binding name="ref-a">
            <remote-destination host="host1" port="7600"/>
        </outbound-socket-binding>
        <outbound-socket-binding name="ref-b">
            <remote-destination host="host2" port="7600"/>
        </outbound-socket-binding>
    </outbound-socket-binding-group>