[Calendar] Free/busy status

[tddang-linagora]

Description

As a user
When I receive an event invitation through calendar
And I open the email containing that event
Then I will see an indicator that will let me know if I'm busy or free at that event's time period

Reference

• https://github.com/linagora/tmail-backend/blob/master/docs/modules/ROOT/pages/tmail-backend/jmap-extensions/calendarEventReply.adoc

Blocking

• Testing environment is non existent.