Delete file when parent entity is deleted

[SimoneZaza]

Description

As a user caring about my data and choosing Alkemio because of its data autonomy policies, I expect that when I remove a reference, the actual file gets deleted too. Same holds for callouts, descriptions, etc., in which I may have uploaded some files. As a user caring about a clean setup, I expect to be able to keep my Space organized by deleting things that are out of date. I do not want files that were uploaded within those things to remain somewhere online.

Acceptance criteria

• [ ] When a user deletes an entity, check if the underlying files are also used elsewhere:
• [ ] If the file is not used elsewhere, delete the file
• [ ] If the file is used elsewhere, do not delete the file

Additional Context

Screen shots / UX designs / data that are relevant.