Bot / API user representing another for pre-filling an application

It could be useful to allow "bots" i.e. API user, to do actions on behalf of another user. For example, after an application is created, a bot could pre-fill some fields on behalf of the applicant.

This can be currently achieved by having the bot use `save-draft` with the applicant user (provided a suitable API-Key), but it may be confusing who did what. Therefore we could have a way to say that this is on behalf of another user, so the event could say "XXX updated the application for YYY" or even "XXX pre-filled the application for YYY".