Missing Transformers initializer for Falcon models

Repro code:
```model5 = keras_hub.models.CausalLM.from_preset("hf://tiiuae/falcon-7b-instruct", dtype="bfloat16")```
Result:
```ValueError: KerasHub has no converter for huggingface/transformers models with model type 'falcon'```

Now that the [Falcon model family](https://huggingface.co/collections/keras/falcon-6720256c00458be2e87b5d05) exists in Keras-hub, this should work.