Add UpgradeTimeout to 04-channel protobuf definitions

[damiannolan]

Summary

UpgradeTimeout defines a type which encapsulates the upgrade timeout values at which the counterparty
must no longer proceed with the upgrade handshake.

message UpgradeTimeout {
    ibc.core.client.v1.Height timeout_height = 1;
    uint64 timeout_timestamp = 2;
}

• timeout_height: Timeout height indicates the height at which the counterparty must no longer proceed with the upgrade handshake. The chains will then preserve their original channel and the upgrade handshake is aborted.
• timeout_timestamp: Timeout timestamp indicates the time on the counterparty at which the counterparty must no longer proceed with the upgrade handshake. The chains will then preserve their original channel and the upgrade handshake is aborted.

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[damiannolan]

#1613