zetaclientd support for multiple RPCs per chain w/ failover

[CharlieMc0]

Each zetaclientd node needs a reliable RPC for each external chain and if that RPC fails it needs to connect a new one. If zetaclient can support multiple RPCs per chain and support automatic failover operators don't need to build their own highly available centralized solutions.

Since the external chain connectivity is critical for ongoing operations it would be good to offer failover capabilities in an easy and decentralized way.