Media: Fixing media folder not getting deleted when deleting media files.

[NillasKA]

Closes #8240

Description

Historically we have "neglected" the media folder that is created on disk when a media item is uploaded, neglected as in never deleting it when deleting the media item.

This fix introduces a lock, that should prevent race conditions when deleting this folder, and also contains a check to ensure that the folder is empty before deleting it.

I have added a Lazy injection of the ICoreScope provider, otherwise it'll create a circular dependency that will leave the application hanging on startup

To test

1. Upload a media item, and observe that a folder is created on disk, containing this media item.
2. Delete the media item from the backoffice (Fully, not just trashed)
3. Observe that the folder is also deleted. Unless it contains more than the media item set for deletion.

[Zeegaan]

Logic seems good to me, but we're missing some tests ;)