New command to delete orphan files

Currently when we remove a file from a resource, the file is not deleted.

This is not a big problem, but it cluters the triplestore with data.

The easiest would be a Moleculer command to remove the triples and the files.

Put it inside MigrationService ?

Start by locating MigrationService and reading the existing paths for removing resource files and their triples. The issue provides no test or file path; done means a Moleculer command removes orphaned triples and files without deleting data still referenced by resources.

Written by the indexing model from the issue text.