Add a Higher Default for thread-pool-max-size in broker.xml

We are seeing performance issues that can be attributed to all of the available ActiveMQ-server-org.apache.activemq.artemis.core.server.impl.ActiveMQServerImpl threads being busy. The broker is optimized for smaller environments, but many users are deploying the broker in environments with dozens or even 100s of applications. The default limit of "30" seems small for production environments. I would propose a higher default, like 100.