Add script to download/sync the models to IA

The Firefox models currently at https://archive.org/details/mozilla-translate-models were downloaded in bulk via python notebook. We want to make this process easy to repeat, so we can update to the latest-and-greatest models as they roll out.

It seems like the models have been moved since the python notebook was made, and are now stored in these locations:

* JSON index of all the models: https://storage.googleapis.com/moz-fx-translations-data--303e-prod-translations-data/db/models.json
* The models themselves: https://mozilla.github.io/translations/model-registry/
* The repo now _doesn't_ contain models, and only contains the code for creating the models. This repo is here: https://github.com/mozilla/translations?tab=readme-ov-file

### Stakeholders

@schu96