docs: @BetaApi
    public final Operation patchRegionInstanceGroupManager(
        String instanceGroupManager,
        InstanceGroupManager instanceGroupManagerResource,
        List<String> fieldMask) {
  
      PatchRegionInstanceGroupManagerHttpRequest request =
          PatchRegionInstanceGroupManagerHttpRequest.newBuilder()
              .setInstanceGroupManager(instanceGroupManager)
              .setInstanceGroupManagerResource(instanceGroupManagerResource)
              .addAllFieldMask(fieldMask)
              .build();
      return patchRegionInstanceGroupManager(request);
    }