Delete a file from the external storage when deleting a resource

[higorspinto]

After deleting an uploaded resource, the resource disappears from the resource list of the related dataset. But after uploading the same file again, the UI displays a message informing that the file already exists in the external storage.

When a user deletes a resource in the edit resource view, the user expects that the resource is also deleted from the external storage.

Steps to reproduce:

1. Create a dataset
2. Create a resource
3. Upload a file
4. Delete the created resource
5. Create a new resource
6. Upload the same deleted file again
7. UI shows a message warning the user that file already exists in the storage.

Acceptance

• Have the file deleted from the storage after deleting a resource.
• It's possible to upload a file that was deleted previously

[higorspinto]

After discussing with @anuveyatsu and @mariorodeghiero, we concluded that the message indicates that the file is already in storage, and we can continue editing metadata and publishing the resource. The action taken here is to display a better message to the user, and it needs to be done in DataPub.