return upstream error code to the client

The codegen for error handling looks like this:

```
if (errors) {
return res.status(400).json(errors[0])
}
```

This doesn't send the `code` received in the `errors[0].extensions` object and only sends the message. Ideally the codegen should send back the error code as it is to the client.

The updated error handling would look like this:

```
if (errors) {
return res.status(400).json( { code: errors[0].extensions.code, message: errors[0].message } );
}
```