Hopeful mechanic to Hall of Fame: Mariano Rivera’s perfect underdog story

One pitch. One team. A 1.000 WHIP, even. Simplicity propelled Mariano Rivera to greatness. Now, however, as he prepares for his official baseball immortalization, the Yankees legend finds himself juggling about a million thoughts. “It’s too much,” a relaxed-looking Rivera said recently in a conversation with The Post at his Westchester home. “It’s too much…