Port ML model publication code from UFCN

Let's port the ci/publish_models.py from UFCN here.

It will be exposed as a subcommand arkindex models publish, and will run the same workflow:

• parse .arkindex.yml
• list all models
• publish them

The main difference with the existing code is that the models must be stored as a tar+zstd archive (first make a tar, then compress with zstandard) to support multiple files in model folders.