Version 3 -> Version 2 bridge/proxy

[EricWittmann]

Consider implementing a proxy that can be a bridge that will accept V3 API calls and bridge them to a V2 server. Useful if you want to upgrade clients to V3 but still run against a V2 server.

[EricWittmann]

This idea came out of the issue with when to upgrade the Registry client support in Kroxy from V2 to V3. But perhaps instead, we can simply support both client versions within Kroxy at the same time.