He’s one heavenly VIP. Late Knicks superfan and Celebrity Row mainstay John F. Kennedy Jr. is cheering on his beloved Knicks from a courtside seat in the sky, a pal told The Post. “I bet he’s cheering from somewhere,” said his close friend and chief of staff, RoseMarie Terenzio. If John John was still alive today, he’d not only be at Madison Square Garden for the NBA finals — he’d be the most popular and best dressed person there, she added. “John was the one New Yorker cool enough to make MSG