x-goog-request-params

We don't generate this:

```js
    options.otherArgs = options.otherArgs || {};
    options.otherArgs.headers = options.otherArgs.headers || {};
    options.otherArgs.headers[
      'x-goog-request-params'
    ] = gax.routingHeader.fromParams({
      parent: request.parent,
    });
```

It should be pretty straightforward, it's described in https://aip.dev/client-libraries/4222.