[train_dreambooth_lora_sdxl] Add --image_interpolation_mode option for image resizing (default to lanczos)

[MinJu-Ha]

related to #11390

This PR adds support for --image_interpolation_mode in train_dreambooth_lora_sdxl.py,
setting the default to lanczos for improved image resizing quality.

This is consistent with the changes made in #11206 to other training scripts.

@asomoza

[MinJu-Ha]

Since train_dreambooth_lora_sdxl.py already has code blocks for lanczos as shown below, I only modified self.transforms part to make use of the parsed interpolation argument.

[asomoza]

yes, indeed I forgot to update that part of the code, thanks!

[HuggingFaceDocBuilderDev]

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[asomoza]

thanks!