Add operation timeout option

[pebo]

We're occasionally seeing very long times (>6minutes) for operations trying to write tiny 90byte files to GCS which then throws the exception mentioned in #833. The services getting the errors are hosted on managed Cloud Run.

The code that (occasionally) triggers the timeout is basically:

    const someObject = { key: "value" };
    const options = {
      resumable: false,
      contentType: 'application/json'
    };
    await file.save(JSON.stringify(someObject), options);

It would be useful to be able to set the timeouts explicitly to a lower value, e.g. 30 seconds rather than 6 minutes.