Luigi Mangione’s wild ride through the justice system stalled out Monday — when he got stuck in a Manhattan court elevator for 20 minutes, delaying a hearing in his federal case. The 28-year-old accused killer of UnitedHealthcare CEO Brian Thompson was in the lift with his escort of US Marshals, headed to the courtroom, when the contraption suddenly stopped, courthouse sources told The Post. “It was some sort of elevator issue, that’s all I know,” Mangione’s lawyer, Karen Friedman Agnifilo, said when asked about the snafu outside the courtroom. “Can’t wait to hear what you guys find out about that!”...