Only connect to nodes as needed

Currently as soon as a kv command is run we fetch a config and connect to all nodes. If a user has a large cluster and is doing a simple get then they're going to pay quite a large penalty here (I'm pretty sure we even connect synchronously). We should connect to nodes according to the keys that we see. This is certainly going to cause complications to do it in a performant way - we'll probably need per node queues or something for whilst a connection is happening. Although we can make that a later optimisation.