Librarians should receive a notification when an item arrives at desk

[ManaDeweerdt]

Describe the bug

For now, the booking notification is sent after a checkin action, when there is a pending loan. This does not completely meet the needs because:

• the request expiration date cannot always be set in the notification (if the item goes in transit)
• some libraries want to print a notification at the moment of the request validation rather than at the request creation

Expected behavior

1. Create a notification at_desk
   • it is sent when a loan arrives "ITEM_AT_DESK" (same condition that triggers the availability notification, with an eventual delay configured)
2. Add a new template for this notification (see below)
3. Adapt the library notification settings to add this notification type. As for availability, it should contain the "delay" field.

Difference with the availability notification

• it is sent to the transaction library, not to the patron
• the template is different (very similar to booking notification, but completed with the request expiration)

TEMPLATE: at_desk.odt OVERVIEW OF NOTIFICATION SPEC: spec_impressions.odt

[PascalRepond]

To me, this is not a bug. By definition a transit or booking notification shouldn't happen on request validation. See specs here: https://bib.rero.ch/help/circulation/#notifications-de-circulation I think this is also what causes misunderstandings in #2707

[pronguen]

This issue has been re-written according to a discussion in the PO group.