Detector idea: flag storage slot usage if contract is upgradeable

### Describe the desired feature

The idea here is that using [EIP-7201](https://eips.ethereum.org/EIPS/eip-7201) should be the recommended best-practice way of managing contract storage of upgradeable contracts. We can push best practice by flagging a finding on upgradeable contracts that store variables in the storage slots at the beginning of the contract (ex: variables listed in `slither --print variable-order`)

Upgradeable contracts can be vaguely identified by the presence of an initialize() function. This would limit false positives to factory-deployed contracts, confidence medium.

We can get better results by checking for inheritance of OZ's UUPSUpgradeable or similar contracts, confidence high.

Severity medium imo, but open to thoughts