Event bus buffer size should be configurable

The current RepositoryChangeBus uses a hardcoded size - 1024 - for its RingBuffer. This might be enough for a simple system, but in the case of a large system which processes lots of events, this size can be increased (though this likely means that some consumers are relatively far behind the latest events).

We should provide a way to configure this value, both from the JSON and WildFly configuration.