The Long Island Musical Theatre Festival gives aspiring performers the opportunity to work under the guidance of Broadway professionals to bring a musical to the stage. This year’s show is John Kander and Fred Ebb’s Cabaret, so guest artist Heidi Blickenstaff, with the help of a bevy of enthusiastic students, sang “New York, New York” at the festival’s Sing Happy: The Songs Of Kander & Ebb cabaret event on July 22.