[IMP] calendar,google_calendar,microsoft_calendar: allow to create events with non-default attendee state

Before this commit, it was not possible to create events with defined attendee state. The default value was always set.
This was a limitation when the events were part of a recurrence and all events attendee needed to be created with a known state.

To reproduce, one would create a recurrent event, sync it with Google and in Google, 'decline' this event and the following.
The attendee state was not properly set.

closes odoo/odoo#68700

Taskid: 2484335
Related: odoo/upgrade#2537
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>