When the WithDiscovery option is passed to PubSub then PubSub will be able to search for more peers that are interested in our topics.
This includes the ability for Publishes (via Topic.Publish()) to block until the router is ready to publish. When a router is ready is currently defined by a combination of a user defined MinTopicSize function (passed into topic.Publish via the WithReadiness publish option) and the properties of the pubsub router used. The discovery tests show example usage.
