Simplify model files architecture when publishing whole parent folder

Most of our models currently stored on Git repos have the following architecture:

- models/model_1/...
- models/model_2/...
- ...

When we port such models to Arkindex, we currently create an archive with the same hierarchy.

- model_1/file_1
- model_1/file_2

It is not practical since the model_1 is not known to the worker. It would be easier to directly have the files without the parent folder.