By the end of Alison Klayman’s Stephen K. Bannon documentary “The Brink”even the most liberal viewer may find themselves rooting for the alt-right agitprop mastermind. In “The Brink,” which opens Friday, Klayman presents a cinema vérité year in the life of Bannon, from the time of his firing from the Trump White House and culminating in the 2018 midterm elections, which saw the Democrats retake the House