Orphan Risk when deleting files from the File-Manager

[ron96g]

Currently files which are managed via the File-Manager are deleted in the Rover-Server, however, this introduces an orphan risk, e.g.

Current Deletion Order:

1. Delete File from File-Manager via FileId
2. if successful, delete CR from cluster
3. Deletion of CR is a no-op in handler
4. if delete of CR fails, fileId points to nothing

Proposed Improvement:

1. Delete CR from cluster
2. Deletion of CR in handler deletes File from File-Manager
3. if successful, remove finalizer
4. CR is deleted

This is a minor issue which only becomes a problem if the k8sClient.Delete(...) in rover-server fails.