chore(model gallery): add gemma-3n-e4b-it

[mudler]

Description

This pull request adds a new entry to the gallery/index.yaml file to include metadata for the Gemma 3n E4B model. The addition provides detailed information about the model's capabilities, efficient parameter management technology, and links to resources for downloading the model.

Added metadata for the Gemma 3n E4B model:

• Model description: Detailed description of the Gemma 3n E4B model, highlighting its multimodal capabilities, efficient parameter activation technology, and training data in over 140 languages.
• URLs: Added links to Hugging Face resources for downloading the Gemma 3n E4B model.
• Overrides and files: Included overrides for model parameters and metadata for associated files, such as filename, SHA256 checksum, and URI.

Notes for Reviewers

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