Why : we had an issue impoting events du to CalendarEvents not yet
existing while inserting the CalendarChannelAssociation due to inverted
method in the service
This PR refactors the calendar event import logic by
- renaming
- splitting utility functions for better clarity and maintainability.
- adding TSDoc comments to explain the purpose and uniqueness of the
`eventExternalId` field in calendar event associations
Fixes#12690
---------
Co-authored-by: Charles Bochet <charles@twenty.com>
6d56b75962