Server Marshallers in MarshallerHelper should support registering additional/extra classes

While developing a KIE-Server extension, I need to register additional (extension specific) classes on the Marshallers. This is possible on a KIE-Server Container level (using KieContainerInstance.addExtraClasses( ... )), but not on a KIE-Server level. This prevents me from using the MarshallerHelper and requires me to manage my own Marshallers.

It would be nice if we can register additional classes on server-wide Marshallers via MarshallerHelper.