Adding support for outbound EventMessage filtering

[bsanders1979]

These are the changes I made to support my use-case of not wanting to publish certain events to AxonServerEventStore to alleviate possible quota issues. I don't anticipate this feature being used outside of the context of migrating to this kind of event store. But, anything is possible I imagine. I was getting errors in DefaultConfigurer and back ported the 4.6 version of code, so you can ignore that bit. I had to check that filteredEvents wasn't empty before passing the value along because it was causing a timeout in my code.

This is how my Spring (non-Boot) config looks now...

public Configuration serverConfiguration(AxonServerConfiguration axonServerConfiguration) {
    return DefaultConfigurer.defaultConfiguration()
        ...
        .configureEventStore(this::buildEventStore)
        ...
        .start();
}

private AxonServerEventStore buildEventStore(Configuration c) {
    return AxonServerEventStore.builder()
       .configuration(c.getComponent(AxonServerConfiguration.class))
       .platformConnectionManager(c.getComponent(AxonServerConnectionManager.class))
       .messageMonitor(c.messageMonitor(AxonServerEventStore.class, "eventStore"))
       .snapshotSerializer(c.serializer())
       .eventSerializer(c.eventSerializer())
       .snapshotFilter(c.snapshotFilter())
       .upcasterChain(c.upcasterChain())
       .eventMessageFilter(event -> event.getPayloadType().getName().startsWith("com.acme.api"))
       .build();
}

[CLAassistant]

All committers have signed the CLA.