chore(model): add magnum-v2-4b-i1 to the gallery

[mudler]

Description

This pull request includes an update to the gallery/index.yaml file to add a new model entry. The most important changes include the addition of a new model with its associated metadata and file details.

Model addition:

• Added a new model entry named "magnum-v2-4b-i1" with a description, icon, and URLs pointing to its locations on Hugging Face.
• Included file details for the new model, specifying the filename, SHA-256 checksum, and URI.

Notes for Reviewers

Signed commits

• Yes, I signed my commits.

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