ADR 006: Implement upgrade client functionality

[Farhad-Shabani]

Summary

There is a requirement for an ADR that explains and justifies the logic behind of upgrade client process. Chains that host ibc-rs may bring different criteria from Tendermint’s, resulting in a different implementation from Tendermint's ibc-go

Proposal

ADR coverage includes:

• Define the boundary between chain-specific operations and general processes
• List all the necessary validation steps
• Specify upgrade client implementation for the Tendermint light client (ics07_tendermint)
• Serve as a reference for those who want to implement this functionality.

Related Issues

• TendermintClient::verify_upgrade_and_update_state is not implemented #19
• Handler for upgrade client #141
• Extract validation step inside new client state creation and expose it as a separate method #384
• Validate "upgrade_client" implementation by adding unit and integration tests #385