title: Get registered devices Google Homegraph
body: <p>Is it possible to receive a list with all registered devices, homes and rooms from a Google account with a google actions? 
  Basically I want to create an action which allows to send notifications to a specific google home device.</p>
  
  <p>I know that this might somehow involve using the Homegraph API. I thought that request sync might do the job but I didn't get it to work. I don't know how to find out the agentUserID.</p>
  
  <p>Anyone experience with using the homegraph API?</p>
  
  <p>Thank you in advance.
  Oli</p>