NEW YORK — Sienna Miller is looking back at putting self-respect center stage — though it didn’t get her very far at the time. The “Anatomy of a Scandal” star, 40, told British Vogue in a new interview that she was once told to “f— off” by an “extremely powerful” Broadway producer when advocating for equal pay. After being “offered less than half” of what her male counterpart would rack up for a weeklong Broadway stint in an unnamed play, Miller recalled telling the producer, also unnamed, “It’s not about money — it’s about fairness and respect.” Though she assumed she’d get the pay increase w…