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