Insiders tell Radar that Pete Davidson is getting serious about becoming a major star and has hired Lady Gaga’s longtime publicist, Amanda Silverman. “Pete never cared about publicity before. Even when he was engaged to Ariana Grande he used the in-house free publicity person at NBC. But that all changed when he started dating Kim, now Pete has brought on his own personal representative,” sources tell Radar. Silverman is a big deal in town representing everyone from Gaga, Mary J. Blige, Bruno Mars, Riley Keough, Ellen Pompeo, Queen Latifah, Rihanna, Amy Schumer, Shakira, Charlize Theron, and J…