Support for AdsDataHub v1

Hello,

Since we are about to use [Google AdsDataHub](https://developers.google.com/ads-data-hub) (ADH), we are in the need to manage some things via API.

We noticed that there is no prebuilt client library for [ADH v1 while it looks like just another Google API](https://developers.google.com/ads-data-hub/reference/rest).

Since this repository is already quite comprehensive in terms of listing what Google API clients can be obtained via Maven packages, why not adding ADH v1?

For the records: We have found a generated client inside of the [Java samples on the guide pages](https://developers.google.com/ads-data-hub/guides/quickstart-api) of ADH. I just wondered whether I did not find it here yet, so it's also running outside of dependency management.

Thanks!