As a user, I want to be able to able to get the code of private contracts I have access to. This is the private equivalent to eth_getCode (https://docs.pantheon.pegasys.tech/en/latest/Reference/Pantheon-API-Methods/#eth_getcode).
Input is the same as eth_getCode (contract address and quantity/tag) + privacy group ID.
Result is code stored at the address if the caller access. Otherwise, null.