Improve tiny model creation script
# What does this PR do?

- Add the option to upload the created tiny models to Hub.
- Make tiny config corresponds better to the (reduced) tokenizer.
  - This gets quite complicated
  - But basically, just to make sure the `vocab_size` and `xxx_token_ids` in the tiny config correspond to what we have in the (reduced) tokenizer. 

Once this PR is approved, should I upload them to `hf-internal-testing`? (I remembered you said yes a few months ago, but want to be sure :-))
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20119). All of your documentation changes will be reflected on that endpoint.