A person of interest has been nabbed in the fatal shooting of UnitedHealthcare CEO Brian Thompson, who was coldly executed in a targeted attack in front of a Manhattan hotel this week, The Post has learned. The man was picked up in Altoona, Pa., using a fake ID, sources said. The bust came amid a massive manhunt for the masked shooter who laid in wait outside the Hilton on Sixth Avenue where Thompson, 50, was set to speak at an investor’s conference Wednesday morning. The chillingly efficient gunman snuck behind Thompson on the sidewalk, pulled out what appeared to be...