Events Backend Cleanup and Adding Start/End Range test (#20633)

* Adding tests in collections and card. Fixing some minor test things

* Added Test for timeline event range selection via card API

* Cleaned up a few TODO comments

* Made the timestamp required when POST-ing a timeline-event

* Remove unnecessary nesting of with-temp* forms

* Moved Icons schema into timeline-event model

This schema seems to be validating more than just the API, so we've moved it.

* Added start/end to GET /api/timeline/:id

Also cleaned up some unnecessary nesting in a card API test
Added timeline range test in timeline API test ns too.

* Parse timestamp when it exists in a timeline-event PUT

We saw the db error presented in the FE when updating timeline events. This should fix that problem.

* Add a test to ensure we can change timestamps via timeline-event PUT