Add Krea 2 LoRA DreamBooth trainer + Krea2 LoRA loader
Adds examples/dreambooth/train_dreambooth_lora_krea2.py and the
Krea2LoraLoaderMixin (Krea2Pipeline now inherits it) so LoRA adapters
can be saved/loaded for the Krea 2 transformer. The transformer/pipeline
forward now accept attention_kwargs for runtime LoRA scaling.
Co-Authored-By: linoytsaban <linoy.tsaban@gmail.com>
