Sets address value to storage admin.
Usage
const newAdmin = "tz1...";
const proxy = await tezos.contract.at(proxyAddress);
const operation = await proxy.methods.setProxyAdmin(newAdmin).send();
await operation.confirmation();
proxy = ContractInterface.from_michelson(code) # or client.contract(contract_address)...
call = proxy.setProxyAdmin("tz1...")
opg = call.inject()