Undeterred by an ambiguous future and declining rents, Related Companies is intent on adding more office space to New York City’s central business district: more than 1 million square feet of it, to be exact. Stephen Ross’ firm last month filed plans for a 1.3 million-square-foot office tower at 514 West 36th Street in Hudson Yards, directly across the street from 66 Hudson Boulevard, where Tishman Speyer is putting the finishing touches on its own