Hersh Goldberg-Polin is on chapter six of the book “The Art of Happiness.” The 23-year-old dual US-Israeli citizen left the tome on his nightstand on Oct. 6, 2023, when he left his family’s home in Jerusalem to attend the Supernova Music Festival near Kibbutz Re’im. In the early hours of Oct. 7, Hamas terrorists stormed the festival, killed 370 people and took 44 more hostage – including Hersh. Six months later, he and 133 others are still held captive in the Gaza Strip. “We are still in a state of incomprehension,” Hersh’s mother, Rachel Goldberg, told The Post. During a...