Support OCI based registries

Onyxia-API currently only supports registries using the "old" `index.yaml` indexing.  
OCI registries does not use `index.yaml` anymore meaning Onyxia-API has no idea how to retrieve the list of packages.  

We should find a way to implement OCI registries support

See discussion on https://github.com/InseeFrLab/onyxia/discussions/909