NEW YORK Liza Minnelli ’s life takes center stage in “Liza: A Truly Terrific Absolutely True Story,” a revealing documentary premiering on April 1 directed by Bruce David Klein, offering an unvarnished portrait of the EGOT-winning icon shaped by talent adversity and five key mentors. Minelli, now 78, overcame addiction, insecurity and the towering legacy of her mother, Judy Garland . “We could have made three dozen different films on her life,” Klein noted. The filmmaker didn't want to do a