The CEO of UnitedHealth was fatally shot in the chest Wednesday morning outside the Hilton hotel in Midtown in what police say was a targeted attack.Brian Thompson, 50, was at the hotel at around 6:46 a.m.when a masked man fired at the CEO and fled eastbound on 6th Avenue, police sources told The Post.Thomas was rushed to the hospital in critical condition, where he was pronounced dead, police said....