It’s just another day on the rails in New York City. An Upper East Side subway rider was photographed wearing a leather strap and chain “cage’’ that was barely covering his genitals  — and was visible to other shocked transit customers — but cops said there is nothing they can do about it. “I’m totally beside myself,” a woman told The Post after trying to file a police report about the sight, which occurred earlier this month on an Upper East Side Q train. “Somehow, this is permissible.’’ She