custom ens registry in ethers-cli

[Amxx]

Some network include a non-official ens deployment, which is not at the "common" address. ethers-ens (from the cli package) can connect to any network, using the --rpc URL option, which is great, but there is currently no way to set the ensregistry.

This would be very usefull to script ens maintenance operations on sidechains and OVM layer 2.