feat(caldav): Sync Reminders / VALARM (#1415)

Co-authored-by: ce72 <christoph.ernst72@googlemail.com>
Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/1415
Reviewed-by: konrad <k@knt.li>
Co-authored-by: cernst <ce72@noreply.kolaente.de>
Co-committed-by: cernst <ce72@noreply.kolaente.de>

pkg/db/fixtures/task_reminders.yml

@@ -12,3 +12,7 @@
   task_id: 2
   reminder: 2018-12-01 01:13:44
   created: 2018-12-01 01:12:04
+- id: 4
+  task_id: 39
+  reminder: 2023-03-04 15:00:00
+  created: 2018-12-01 01:12:04