Handler for upgrade client

[adizere]

Crate

ibc

Summary

• handler implementation in ics02_client::handler::upgrade_client.rs
  • raise an issue with cosmos/ics to add canonical algorithm for handling this message? not clear if that's desirable since this is documented and handled mostly in the SDK: https://github.com/cosmos/cosmos-sdk/tree/master/docs/ibc/upgrades
  • probalby inspired from Upgrade Client cosmos/cosmos-sdk#7367 since there is no canonical algorithm in the cosmos/ics spec (yet)
• clarify the use of upgrade_path field in Tendermint client state and include that in tests

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[hu55a1n1]

Transferred (manually) to cosmos/ibc-rs#141