Check ActiveStorage setup

[MrSerth]

Lately, we encountered a few issues with attachments through ActiveStorage. Thus, we should validate our integration:

• Ensure files get removed completely through ActiveStorage. This includes:
  • Deleting the attachment (keeping the record otherwise) removes the database entry (in internal ActiveStorage tables) and the file on disk.
  • Completely removing the record also removes database entries and files.
  • All relevant files (i.e., resized images) are considered.
• Provide a simple script to check that all files in /storage are referenced in the database and vice versa. Further, each object referenced in the internal ActiveStorage tables should still exist and not be soft-deleted (users!). This script is intended to run on production once.