This is the most important piece because this contract will never change. We don't want it to change, because we want to keep the same Ethereum address while updating the underlying logic. This contract will redirect all the calls to the upgradable contract and will have several variables to register the current upgradable contract's address and a list of past contracts for those that don't want to update to the new code.
Remember that upgrading to a new version is always optional. If your users decide that they want to keep using the old smart contracts, they will simply send all their transactions to the old upgradable contract directly without executing the proxy contract. You could stop them from doing so by destroying ...
