code: @BetaApi
    public final ListInstanceGroupsPagedResponse listInstanceGroups(ProjectZoneName zone) {
      ListInstanceGroupsHttpRequest request =
          ListInstanceGroupsHttpRequest.newBuilder()
              .setZone(zone == null ? null : zone.toString())
              .build();
      return listInstanceGroups(request);
    }
docs: Retrieves the list of instance groups that are located in the specified project and zone.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceGroupClient instanceGroupClient = InstanceGroupClient.create()) {
  ProjectZoneName zone = ProjectZoneName.of("[PROJECT]", "[ZONE]");
  for (InstanceGroup element : instanceGroupClient.listInstanceGroups(zone).iterateAll()) {
  // doThingsWith(element);
  }
  }
  </code></pre>
  
  @param zone The name of the zone where the instance group is located.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails