Refactor to account for upstream changes in ibc-go 02-client refactor

[jtieri]

We will need to account for some upstream changes in ibc-go following their completion of the refactor to the 02-client codebase. Creating this issue to keep track of changes that will need to be made in the relayer.

Loose item checklist

• ibcexported.Header will be replaced by ibcexported.ClientMessage throughout the entire codebase
• clienttypes.PackHeader() will be removed and replaced with clienttypes.PackClientMessage() see

References:
cosmos/ibc-go#1202 (comment)
cosmos/ibc-go#1107

[jtieri]

Alpha release for the 02-client refactor has been cut https://github.com/cosmos/ibc-go/releases/tag/02-client-refactor-alpha1

This should allow us to begin the process of refactoring to account for the new changes. We could probably start to introduce some unit tests around introduction of the beefy light client

[jtieri]

Updating with new info regarding the 02-client refactor.

Updates to ICA have been prioritized over this refactor which has pushed the expected date for this to November.