Review and improve the process, testing and CI for gateway upgrades

[lumtis]

Our current testing suite for smart contract upgrades:

• The ZetaChain E2E that perform a gateway upgrade and run the CCTX E2E tests
• The tool https://github.com/zeta-chain/protocol-contracts/tree/main/scripts/deploy#simulating-a-protocol-contract-upgrade to simulate an upgrade on a live network from a deployed address

The next upgrade will bring extensive changes with the ZETA token support on gateway, we should therefore review our current process and check for any improvement to ensure the maximum security standards for the gateway upgrades.

We might consider the following:

• Adding https://github.com/zeta-chain/protocol-contracts/tree/main/scripts/deploy#simulating-a-protocol-contract-upgrade as part of the CI
• Having more extensive tests to check for storage layout breaking changes in the protocol contracts