Investigate Better Calendar Invite Integration with Other Calendar Providers

[wrdhub]

Issue: When someone creates an event on a non-Tuta Calendar and invites a Tuta address, the way we respond with attendee status does not update the attendee status.

Main platforms to check: iCloud Calendar, Google Calendar, Outlook, and Proton Calendar.

Questions: Why isn't the response updating the attendee status? Is there something that we can change to make this work? Are these changes practical and in line with our security/privacy ideals? How are responses sent from other platforms? Do our events get updated with the attendee status?