Line finding scripts (from O3 magnetar search)

Added line finding scripts from O3 magnetar search. Probably need to be generalized and updated. Files are here: https://git.ligo.org/adrian.macquet/pystampas/-/tree/master/scripts/lines. Git issue from O3 magnetar paper is here: https://git.ligo.org/publications/O3/o3-magnetar-burst/-/issues/14. Overview is here: https://git.ligo.org/ryan.quitzow-james/o3_magnetar_search/-/blob/master/line_notes_v2.md.