Rule 2104. Stipulations. An agreement between parties or their attorneys relating to any matter in an action, other than one made between counsel in open court, is not binding upon a party unless it is in a writing subscribed by him or his attorney or reduced to the form of an order and entered. With respect to stipulations of settlement and notwithstanding the form of the stipulation of settlement, the terms of such stipulation shall be filed by the defendant with the county clerk.