The Fenimore ROCKS! Museum’s Biggest ShowTo Feature Photos Of Madonna,Cher, All Of Rock’s Greatest By LIBBY CUDMORE COOPERSTOWN Madonna is coming to Cooperstown.So is David Bowie. Bob Dylan, Bruce Springsteen and Tina Turner will be here too, part of “Herb Ritts: The Rock Portraits,” due to open April 2 at The Fenimore Art Museum.“There are more than 100 pieces to this collection,” said curator Chris Rossi. “It’s the largest show we’ve ever put on.” Ritts’ “Rock Portraits” debuted at the…