MONTREAL—Rowdy fans outside the Bell Centre were already celebrating—cheering and launching fireworks—before the Montreal Canadiens beat the Vegas Golden Knights to advance to the Stanley Cup final for the first time since 1993 on Thursday. Artturi Lehkonen scored in overtime as Montreal edged Vegas 3-2 to take the third-round series in six games, with the goal setting off wild scenes of unbridled joy both inside and outside the Bell Centre. Outside the arena, where mobile internet connections were poor, few people appeared to know who had scored the game-winning goal, only that their team had won, as fans hugged each other, danced in the streets and chanted “olé, olé, olé” and “go Habs go!” Following the game, fans were temporarily forced to stay inside the arena due to safety concerns as the streets in the nearby area became raucous. Police began firing tear gas into the crowd surrounding Bell Centre …