Could we have dialogflow FulfillmentWebhookClient imported and maintained into this repo?

**Is your feature request related to a problem? Please describe.**
There is https://github.com/dialogflow/dialogflow-fulfillment-nodejs/ repo which it said it not maintained. It still work and should be updated as of dialogflow being update

**Describe the solution you'd like**
Please include the `WebhookClient` into dialogflow npm package. Maybe rename it into `FulfillmentWebhookClient` and reuse the same response object as `IntentsClient`. So we could use `Card` and other response object as returned fulfillment

**Describe alternatives you've considered**
Still maintain that old repo maybe? I would prefer using `Card` and other class in this repo as fulfillment though