Cosmos-sdk: Allow chains to white/black-list IBC client types

[AdityaSripal]

Chains should be able to use governance to whitelist/blacklist client types that they will accept as clients on their own chain.

This is important so that chains that do not trust the implementation/security model of a particular client type can opt-out of supporting it without forking the SDK

[cwgoes]

This is important so that chains that do not trust the implementation/security model of a particular client type can opt-out of supporting it without forking the SDK

This is fine, but it's worth noting that chains themselves are never exposed to faults from other chains, only users who elected to send assets over bridges (or equivalent application protocols).

[colin-axner]

Sounds fine to me. We should use allow/disallow list naming

[colin-axner]

This is important so that chains that do not trust the implementation/security model of a particular client type can opt-out of supporting it without forking the SDK

Another approach would have been making a more modular process for including or not including clients being registered on the codec? That way chains could just do this at genesis, it wouldn't allow for it to be changed via governance though