Currently when changing category of an event, its category mail scheduling
is copied onto the event even if the category does not enforce its use.
We have to check the category use_mail_schedule field before computing
the new event mail schedulers.
In this commit we also lessen default schedulers from 3 to 2 in order to
still help people using them without bloating too much event creation.
LINKS
Task ID 2177281 (support tickets directly in event)
Prepares Community PR odoo/odoo#43488
Closes Community PR odoo/odoo#44066
Thibault Delavallée
3b1c2566ed