As a young boy, Judd Apatow says he wanted to grow up to be like Mel Brooks, the filmmaker of such comedy classics as “Blazing Saddles” and “Young Frankenstein.” Now Apatow has co-directed a two-part HBO Max documentary about his idol, “Mel Brooks: The 99 Year Old Man!” Apatow talks with Tracy Smith about the World War II veteran who broke comedy taboos by lampooning Nazis and racists, and about Brooks’ long friendship with another comic legend, Carl Reiner.