feat: Calendar Import

[SebastianKrupinski]

Summary

This adds the ability to import calendars

Split of #49995

OCC Import

Command: calendar:import
Arguments:
uid - mandatory
cid - mandatory
format - optional defaults to ical (ical, xcal, jcal)
filepath - optional defaults to stdin
--supersede - optional (force override of existing)
--show-created - optional (show uid of created objects)
--show-updated - optional (show uid of updated objects)
--show-skipped - optional (show uid of skipped objects)
--show-errors - optional (show uid of objects with errors)
--errors (int) - optional - how to handle errors (0 - continue, 1 - fail)
--validation (int) - optional - how to handle item validation (0 - no validation, 1 - validate and skip on issue, 2 - validate and fail on issue)

Import from file:

calendar:import user1 personal ical /tmp/personal.ics

Import from pipe:

cat /tmp/personal.ics | calendar:import user1 personal ical

Import from file and override existing:

calendar:import user1 personal ical /tmp/personal.ics --supersede

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)