When Katy Perry joined American Idol in 2018, she became the highest-paid judge on the show with her $25 million per year salary — which is why it’s hard to believe that while growing up, the singer and her sister didn’t even always have food on the table. “You want to talk about food stamps? I can talk about food stamps. You want to talk about food banks? I can talk about food banks,” explained Perry, 39, in a new interview. “You want to talk about busking in the street as a teenager, hoping to make $20 to cover yourself, I can talk about that too.” The siblings’ experience is what prompted t…