Houston Rockets owner Tilman Fertitta made stock purchases that could be worth as much as $420 million. David J. Phillip/APThe United States’ ambassador to Italy just made a massive personal gamble on casinos.Billionaire diplomat Tilman Fertitta, who owns the NBA’s Houston Rockets and dozens of restaurants and hotels, has purchased at least $113 million in Caesars Entertainment since November, new federal financial documents reviewed by NOTUS in…