WIP: Rackconnect v3 Load Balancer Pool support

This provides API support for RackConnect V3 load balancers.  First ask of #104 
Minor nitpick: I don't know if there's an interesting use case for setting empty regions, but that'd be foiled by this check, of course :-) Suggestions: `regions=("ORD",)` or `self._regions = regions if regions is not None else ["ORD"]`.