Update copilot instructions

[shirasassoon]

This pull request significantly restructures and expands the .github/copilot-instructions.md documentation to provide a clearer, more actionable guide for developers working with the fabric-cicd Python library. The changes focus on improving quick-start usability, clarifying authentication requirements, introducing configuration-based deployment, and outlining development/testing best practices.

Key documentation improvements:

Quick Start & Validation:

• Replaces the verbose setup and validation sections with a concise "Quick Command Reference" table, listing essential commands, timeouts, and mandatory validation steps for development and CI.

Authentication Guidance:

• Clearly explains authentication requirements, emphasizing explicit use of the token_credential parameter, and provides concrete examples for local development, CI/CD, and testing scenarios.

Deployment Methods & Project Structure:

• Adds a new section on config-based deployment using deploy_with_config(), including references to implementation files and tests.
• Restores and updates the project structure diagram for easier navigation.

Development & Testing Guidelines:

• Details core development patterns, publisher class structure, serial publishing, parameterization, and best practices for adding features or tests.
• Outlines testing strategies, types of tests, and use of mocks for external dependencies.

Pull Request & Troubleshooting Standards:

• Specifies strict PR title formatting, validation requirements, and troubleshooting steps for common agent and CI issues.
• Highlights key files to monitor for changes and provides references to example directories and documentation.

These changes make the documentation more accessible, actionable, and maintainable for both new and experienced contributors.

Most important changes:

Documentation Structure & Usability

• Replaces lengthy instructions with a clear "Quick Command Reference" table, streamlining setup, validation, and CI/CD workflow steps.
• Restores and updates the project structure diagram for easier navigation of the codebase.

*Authentication

[Copilot]

Pull request overview

Updates .github/copilot-instructions.md with normalized list formatting and two new documentation sections: config-based deployment guidance and a detailed checklist for onboarding new Microsoft Fabric item types.

Changes:

• Normalized markdown list syntax from - to - throughout the file
• Added "Config-Based Deployment" section documenting deploy_with_config() API usage
• Added "Onboarding New Item Types" section with step-by-step instructions for extending the system