Support RefinedWebModel as a model_type for Falcon
This PR allows us to temporarily revert the model_type for Falcon repos to fix some issues.

cc @sgugger @LysandreJik @Narsil @OlivierDehaene @slippylolo 
No this is not enough. If we go down that road we need to erase the `RefinedWeb` model type on loading to replace it with `falcon`, so that a new saved version does not keep it.<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>This already happens! The model type that is saved in `config.json` is set in `configuration_falcon.py`, with the line `model_type = "falcon"`. If you load a model with model_type `RefinedWebModel` and save it, the output `config.json` has model_type `falcon`.<|||||>Closing because just changing the `model_name` field won't be enough anyway - we also need to revert all the `config.json` parameters.