Add API to aztec.js for batching actions

[spalladino]

While our account contracts support batching actions, the API for this is super awkward. It should be easier to go from a set of ExecutionRequests to a SentTx object.

const actions = [
  contract.methods.transfer(10, owner, recipient).request(),
  contract.methods.withdraw(owner, 20, recipient).request(),
];

const nodeInfo = await wallet.getNodeInfo();
const txContext = TxContext.empty(new Fr(nodeInfo.chainId), new Fr(nodeInfo.version));
const txRequest = await wallet.createAuthenticatedTxRequest(actions, txContext);
const tx = await wallet.simulateTx(txRequest);
const sentTx = new SentTx(aztecRpcServer, wallet.sendTx(tx));
await sentTx.isMined();