Add RCv3 service name to config

This adds this as hardcoded config, which is the way it works now. Ideally, it should eventually do something else, but that's not a problem we're gonna solve right now.
For the key, or the value? Obviously for the value, we don't get to pick; it's whatever it is in the service catalog. I believe that is `rackconnect`. For the key, I'd prefer to stick to the already set habit of "default to the value it probably ought to be"; I agree that I'd rather have `RackConnectV3`, but I'd also rather have `CloudServers`, not `cloudServersOpenStack`.

That said, I think actually checking that this is in fact the service name would be a good review point :)