WebSocketsDefinition BUFFER_POOL and WORKER are not configured as capability references

This makes it hard to remove or rename the 'default' worker (e.g. as part of doing performance tuning), because the requirement for that worker isn't shown in standalone.xml. Since there's no capability ref failure, boot proceeds to RUNTIME, ServletContainerService can't start but a whole lot of others can't start as well. So there's a lot of noise that obscures the issue.