feat: Set Kale as Default Kubeflow Notebook Image

### Feature Area

/area backend

### What feature would you like to see?

Make Kale available as a default Kubeflow notebook image, with an option for admins to set it as the preselected image when creating notebooks.

Goals
- Reduce setup friction for new users
- Provide a consistent Kale-enabled environment

### What is the use case or pain point?

To improve the Kubeflow ecosystem, Kale should be available by default in Kubeflow Notebooks, but currently, users must manually enable it. This adds friction and leads to inconsistent environments, especially for new users.

### Is there a workaround currently?
Yes. Users can install Kale via pip inside the notebook or use a custom image. Both approaches are manual, error-prone, and not consistent across sessions or teams.

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The issue names no files, tests, or entry points. Start by locating the Kubeflow Notebook image configuration and the notebook-creation path for admin image selection, then review existing tests there. Done means Kale is available as a default image and administrators can set it as the preselected image.

Written by the indexing model from the issue text.