Loading dataset from disk where it exists

In these scripts [[1](https://github.com/huggingface/diffusers/blob/main/examples/text_to_image/train_text_to_image_lora.py)] [[2](https://github.com/huggingface/diffusers/blob/main/examples/text_to_image/train_text_to_image.py)], loading a dataset that is saved with `save_to_disk` throws an error, and one is forced to use a dataset from the HF hub

Start by reading the dataset-loading paths in examples/text_to_image/train_text_to_image_lora.py and examples/text_to_image/train_text_to_image.py. Reproduce the failure with a dataset saved through save_to_disk, then verify that both scripts can load that local dataset without requiring a dataset from the Hugging Face Hub.

Scritto dal modello di indicizzazione a partire dal testo della issue.