[TT-027] Export task as calendar file (ics)

[NarrowCode]

As a user with a calendar

I want to be able to export a task by clicking a button that opens my calendar application where I can store it as an event

so that I don't have to manually add it

Details: It will probably be sufficient to notify the Android OS with a request to "open" a temporary .ics file, after which the default calendar application should take care of the rest, if the file is formatted properly. Should be researched before starting implementation.

Example .ics file content:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:TodoTasker
CALSCALE:GREGORIAN
BEGIN:VTIMEZONE
TZID:Europe/Berlin
TZURL:http://tzurl.org/zoneinfo-outlook/Europe/Berlin
X-LIC-LOCATION:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:20210519T091256Z
UID:20210519T091256Z-1781177204@marudot.com
DTSTART;TZID=Europe/Berlin:20210520T110000
DTEND;TZID=Europe/Berlin:20210520T120000
SUMMARY:Test1
DESCRIPTION:Descr
END:VEVENT
END:VCALENDAR

Acceptance criteria

• [ ] User can click on the (...) menu in the modify dialog -> "export to calendar"
• [ ] On clicking "export to calendar", the file is opened by the users calendar application of choice