Abrupt interaction when trying to add a thesaurus item on an empty group thesaurus

[hyebin-bina]

1. User creates a group thesaurus without adding children items.
2. User goes back to the thesaurus and tries to add items afterwards.
3. The editing box abruptly gets closed as soon as user clicks the "Add" button without any disclaimer or error message, giving the impression that the system is throwing an error (see the attached screencast).

If our intention is to allow grouped thesaurus only when there are children items, we should prevent the users at an earlier stage when they try to save without putting the children items.

https://github.com/huridocs/uwazi/assets/85096417/f661826a-d9d3-4fa8-b560-6910cbc9c432

[RafaPolit]

This is also reported as the Thesaurus V2 roadmap here: #6699 and #6696

The real issue here is:

Empty Groups, if they have no children, are treated as "root non-group elements".

This should use similar validations as in filters, where creating and empty group disables the save until you actually put a value in it.

[aphilop]

Closing this as duplicate to https://github.com/huridocs/uwazi/issues/6696