It is in the localisation files
To test I searched for "obj_help_friend_job" and found it in V21.csv, the string for "title_cupbearer" is in vae_victis.csv. You can probably just add your new objectives in a new file with a name of your choice if you wanted to.
Rather new to this game but this triggers all of the time for me as Carthage
Not quite as common as "become ruler", "become rich" or "rivals death" but it probably ranks after those.I've also seen plenty of characters with the ambition to become cupbearers, etc in the same game (it's a quite common ambition among the envoys that numidia sent me).