One way or another, the Cubs will feel good about themselves when they step on the field to face the Dodgers or the Mets in the National League Championship Series, beginning Saturday. They would be fine to play with their backup shortstop, Javier Baez, in the middle of their infield. But 21-year-old Addison Russell is the guy who has earned the chance to be introduced with manager Joe Maddon’s starting lineup.