Richard Avedon got his first assignment from Harper’s Bazaar in 1944, when he was 21 years old. For the next six decades, his coverage of fashion, fame and cultural revolutions created a peerless iconography. His work has been recognized over the years in huge museum retrospectives, so much so that you might have expected the centenary of his birth on May 15 to occasion a massive institutional blowout from the likes of the Metropolitan…