Deleting datasets triggers SQL foreign-key violation

[fm3]

Users deleting datasets for which annotations exist triggers an SQL foreign-key violation
Detail: Key (_id)=(61fd361a010000e600f41f29) is still referenced from table "annotations".
We should discuss what the behavior should be here (can the annotations somehow stay downloadable?).

[fm3]

in case an annotation referencing the DS exists, only delete on disk, but not in postgres (instead, mark as deleted)

annotations should still be downloadable