Conflict of jurisdiction between an arbitration tribunal and the judiciary. Possibility of direct enforcement of an extrajudicial enforcement instrument containing an arbitration clause. Matters relating to motions to stay execution and third party motions to prevent encumbrance or disposition of property concerning the instrument or the obligations set forth therein (existence, constitution or extinction of the credit) and matters elected by the parties to be resolved by the arbitral tribunal fall within the jurisdiction of the arbitration tribunal: