“The Gatekeepers,” a new documentary by the Israeli director Dror Moreh, consists of interviews with six men, all of them retired, most of them bald, one of them a grandfatherly type, well into his 80s, in suspenders and a plaid shirt. They reminisce about past triumphs and frustrations, but Mr. Moreh’s amazing, upsetting film, which opens Monday for a weeklong awards-qualifying run in advance of a wider release next year, is the opposite of nostalgic. It is hard to imagine a movie about the Middle East that could be more timely, more painfully urgent, more challenging to conventional wisdom on all sides of the conflict.