City officials are arguing over whether a residential development in the Flatiron District’s Ladies’ Mile Historic District should be forced to include affordable units. The decision could have broader implications for the de Blasio administration’s zoning plan. The Mendlowits family, affiliated with the entity 42 West 18th Street Realty Corp., requested a special permit form the city planning commission to build a 188,800-square-foot mixed-use building with 66 market-rate apartments on the lot.