Use `HfApi` instead of `Repository` in training scripts

[pcuenca]

Repository is being deprecated, but we still use it in a couple of training scripts:

• diffusers/examples/dreambooth/train_dreambooth_flax.py

  Line 19 in 4d2c981

  from huggingface_hub import HfFolder, Repository, create_repo, whoami

• diffusers/examples/unconditional_image_generation/train_unconditional.py

  Line 19 in 4d2c981

  from huggingface_hub import HfFolder, Repository, create_repo, whoami

Research projects:

• diffusers/examples/research_projects/onnxruntime/unconditional_image_generation/train_unconditional.py

  Line 17 in 4d2c981

  from huggingface_hub import HfFolder, Repository, create_repo, whoami

• diffusers/examples/research_projects/intel_opts/textual_inversion_dfq/textual_inversion.py

  Line 16 in 4d2c981

  from huggingface_hub import HfFolder, Repository, whoami

Docs:

• https://github.com/huggingface/diffusers/blob/4d2c981d551566961bbc7254ae9556d76dd95764/docs/source/en/tutorials/basic_training.md?plain=1#L287C43-L287C53
• ko translation of above

cc @Wauplin

[Wauplin]

Thanks for opening the issue @pcuenca! If it can help, here is the PR in transformers that removed Repository in training scripts: huggingface/transformers#25095.

[patrickvonplaten]

Cool, @sayakpaul do you have time to update our examples here maybe?