BIG-IP DNS Forwarder Support via iRule

note that the iRule will rotate forwarding queries between the IPs listed in the datagroup, but it doesn't do anything to track whether or not there is a response and retry it to the other server. The expectation is that the client submitting the request to the listener would resubmit the query. It should be possible to implement some timeout/retry logic in the iRule, but for now, that is to be completed/explored.