[IMP] google calendar: auto accept meeting when only creator is attendee

Before this commit, when an event containing only the creator was created in Google Calendar, the creator's attendee status in Odoo was marked as 'needsAction'. Now, when an event like this is created (in Google Calendar), the event is automatically accepted in Odoo.

A test was added to make sure that new events with only the creator are automatically accepted.

closes odoo/odoo#112179

Task: 2782961
Related-to: #68700
X-original-commit: 6d0ead3d73477614dc1bd97a95b695f80925fdd3
Signed-off-by: Arnaud Joset <arj@odoo.com>