[train_dreambooth_lora_lumina2] Add LANCZOS as the default interpolation mode for image resizing

[cjfghk5697]

What does this PR do?

Fixes #11390

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

This PR sets LANCZOS as the default interpolation method for image resizing during training, improving visual quality and preserving fine details in training inputs.
Users can still override it with --image_interpolation_mode bilinear for faster processing if needed.

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[asomoza]

thanks!