We need to send transactions to a specific query node

So – after a BEGIN WORK call, all subsequent queries for that transaction attempt need to be sent to the same query node that responded to that BEGIN WORK call. Ideally, we'd have an optional field in the query_request specifying the node to send the request to.

Probably there needs to be some errors handling around that node no longer being available, etc... as well.

Blocks transactions 2.1 - though as long as there is just one query node, we can continue developing that work.