[OpenVINO] Add agentic skill for adding new model support

[rkazants]

What does this PR do?

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[HuggingFaceDocBuilderDev]

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[Copilot]

Pull request overview

This PR adds an agentic skill documentation file that provides comprehensive guidance for adding support for new model architectures from HuggingFace transformers and diffusers libraries to the optimum-intel project. The skill enables model export to OpenVINO IR format and inference through the optimum-intel API.

Changes:

• Added a detailed skill documentation file (skills/SKILL.md) containing workflows, code examples, and reference materials for implementing new model support in optimum-intel
• Included practical examples for model architecture analysis and patching patterns (particularly Mixture of Experts)
• Provided references to test files, documentation locations, and external resources

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