code: @BetaApi
    public final Operation attachDiskInstance(
        String instance, Boolean forceAttach, AttachedDisk attachedDiskResource) {
  
      AttachDiskInstanceHttpRequest request =
          AttachDiskInstanceHttpRequest.newBuilder()
              .setInstance(instance)
              .setForceAttach(forceAttach)
              .setAttachedDiskResource(attachedDiskResource)
              .build();
      return attachDiskInstance(request);
    }
docs: Attaches an existing Disk resource to an instance. You must first create the disk before you
  can attach it. It is not possible to create and attach a disk at the same time. For more
  information, read Adding a persistent disk to your instance.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceClient instanceClient = InstanceClient.create()) {
  ProjectZoneInstanceName instance = ProjectZoneInstanceName.of("[PROJECT]", "[ZONE]", "[INSTANCE]");
  Boolean forceAttach = false;
  AttachedDisk attachedDiskResource = AttachedDisk.newBuilder().build();
  Operation response = instanceClient.attachDiskInstance(instance.toString(), forceAttach, attachedDiskResource);
  }
  </code></pre>
  
  @param instance The instance name for this request.
  @param forceAttach Whether to force attach the disk even if it's currently attached to another
  instance.
  @param attachedDiskResource An instance-attached disk resource.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails