Permissioned Contract Upgradeability

[phutchins]

• Pick an upgrade pattern, see this post and updates here
• Consider what's popular in the ecosystem and supported by tooling, such as Etherscan, Tenderly, etc...
• Keep in mind that the upgradeability pattern we choose will be applied to multiple contracts in the dgrants protocol
• Leave a comment on this issue summarizing leading patterns, their tradeoffs, and a decision (if you have one)