title: Automatically generate google-services.json for Android flavor
body: <p>I have an app which I need to add different flavors, and each flavor must have the google-services.json file from firebase. 
  It means that now I manually register a new application, download the json file and put it in the flavor project (folder).</p>
  
  <p>Is there any API for registering the flavor app (different package name) manually, 
  downloading it, and put it in the correct folder, during the gradle build process, by using gradle tasks?  </p>