Add logic to unfreeze frozen / expired clients

[seanchen1991]

Problem Statement

As part of implementing ADR-026 in ibc-rs, a frozen/expired client is recovered by updating it to match a substitute client.

Once the substitute client has been validated by ClientStateValidation::check_substitute, the subject client is updated such that its state matches the latest state of the substitute client.

Proposal

Implement the ability for a subject client to be updated to match the latest state of a substitute client, either in the ClientStateExecution::update_state function, or in a new function that is added to the ClientStateExecution trait.