It’s a first for a first lady. Melania Trump’s documentary, “Melania: Twenty Days to History,” is getting a lavish Washington, D.C., premiere at the Kennedy Center on Thursday before rolling out on more than 1,500 screens in the U.S. and Canada this weekend. The film, which follows her life in the run-up to last year’s inauguration, has few precedents. As a movie, it is one of the few political documentaries to receive a wide release. As a political object, it’s the first time a sitting first