Delete related attachment & images when an entity is deleted

[joelvdavies]

When a catalogue item, item or system is deleted. Any attachments/images should also be deleted. Will likely need either

• The following tasks

  • Add an endpoint for getting a list of attachment metadata object-storage-api#25
  • Add an endpoint for getting a list of image metadata object-storage-api#36
  • Add an endpoint for deleting an attachment object-storage-api#28
  • Add an endpoint for deleting an image object-storage-api#38

• Or an additional task that takes the entity and deletes all relevant attachments and images at once (Perhaps a DELETE /entity/<entity_id>)

• Need to consider

  • What happens if deletion is not possible due to a connection issue? - would also relate to handling of e2e tests
  • How will authentication between the services work?