NEW massaction Clone eventattendees to event

[JonBendtsen]

NEW #37954 massaction Clone eventattendees to event

This PR adds a new massaction to clone eventattendees from one event to 1 or more other event(s). During cloning you can independently change status of both new attendee object and old attendee object - though only to the same for all event attendees and the same in all the receiving events. The default value is to keep the old status when creating the new event attendee, and not change the old event attendee status.

This even works if you select a list of event attendees with mixed status, the new event attendee objects by default get the same as the old, even if other event attendees in the selection has a different status.

This PR be default has selected a checkbox that adds an object link between the source and the clone, and when looking at the card of these event attendees, it even shows the translated text for either source or clone, even depending on which direction you look at the links.

Triggers can be disabled, and that is the default value since this is a massaction.

This massaction cloning could be used for registrations on a waiting lists that you transfer to next event.

This PR would almost close #37954, as it does not handle single object cloning.

[JonBendtsen]

screenshots

Selection and start of massaction clone

massaction cloning form

normal cloning results popup

verbose cloning popup

Popup with errors after clone worked, but changing status and project did not

source attendees list after cloning

cloned attendees list after cloning

WARNING duplicates are easily possible

the individual attendee cards shows linked objects depending on the direction of the link