Clean up /assets_generation

[reyammer]

The current way of dealing with assets is as follows:

• the training pipeline exports all relevant assets (content types KB, models, etc.) to the /assets directory.
• the python and rust codebases have a sync script that pulls whatever is relevant for them from the /assets directory.

This allows us to keep python (or rust) related codebase in their dedicated directory (e.g., /python).

We need to clean up the following aspects related to /assets_generation:

• it has code that considers the assets and generates additional ones (e.g., a README for the model)
• it has code that generates js-related assets, such as the tfjs model and config. Ideally these belong somewhere else.