upgrades: make sure that relaying works across upgrades

[erwanor]

Is your feature request related to a problem? Please describe. We should test that ordinary chain state upgrades are not light-client breaking. This should be tested by pointing a relayer to a chain that undergoes a simple upgrade and make sure that there are no errors across the upgrade boundary.

Context: Upgrades that are light-client breaking should be rare, and require a special IBC mechanism (#3356). We want to make sure that we haven't missed something that would make ICS07 clients incapable of verifying our chain state post-upgrade.

Blocked: We will only be able to test this once we have completed #3506.