ST. LOUIS — Doug Glanville has played center field. He has played for the Cubs. As one of the most thoughtful observers of baseball, he can offer an insider’s perspective on what it is to be Pete Crow-Armstrong. ‘‘I’ve had a lot of chances to talk to him,’’ Glanville said, sitting in the visitors’ dugout Sunday afternoon at Busch Stadium, while in town to serve as an analyst on ESPN’s radio broadcast of the Cubs-Cardinals game. ‘‘I’m always very…