It took two decades for Laura Poitras , the director of Oscar winner “Citizenfour” and Oscar nominee “All the Beauty and the Bloodshed,” to convince Pulitzer-winning journalist Seymour Hersh to let her make a film about his career. The long-gestating project finally became a reality three years ago, with Hersh allowing Poitras and co-director Mark Obenhaus, a long-time friend of his, full access to his archives. The result of the monumental work of research and months of in-depth interviews is “