Add LoRA Finetuning for Würstchen

[dome272]

Is your feature request related to a problem? Please describe.
It would be nice to easily finetune Würstchen using Diffusers which we released yesterday with this blog post

Describe the solution you'd like
Since you can already finetune SD models with LoRA it should be fairly easy to adapt I believe to make it work with Diffusers.

[github-actions]

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