Issuing a compact request requires a dedicated message. Define a new message:

public final class CompactSubtreeRequest extends Request<TransactionIdentifier, CompactSubtreeRequest> {

   public final @NonNull YangInstanceIdentifier getPath();
}

and its corresponding replies. Since this is a new API, also define a new ABI version, so that the use of this message is properly gated.

Use this message if the shard that we connect to advertizes the appropriate ABI version – and also which to no-op when it does not.