Add Calendar API endpoint to get events (#14702)

* Add Calendar API endpoint to get events

* Set default event color

* Fix PR comments

* Fix PR comments

* Fix PR comments

* Remote local.py file

* Use iso 8601

* Fix lint

* Fix PR comments

* Fix PR comments

* Add Support for todoist and demo calendar

* Todoist events are allday events

* Add calendar demo api endpoint test

* Register only one api endpoint for calendar

* Rename demo calendar