Create CODEOWNERS file for code ownership and review assignment

[Copilot]

This PR creates a CODEOWNERS file to establish clear code ownership and enable automatic review assignment for pull requests in the DefangLabs/defang-github-action repository.

What's Added

The .github/CODEOWNERS file defines ownership rules for different parts of the codebase:

• Global ownership: @lionello and @DefangLabs/maintainers for all files by default
• Action definition: @lionello and @edwardrf for the core action.yaml file
• Documentation: @raphaeltm and @lionello for README.md, @lionello for LICENSE
• CI/CD workflows: @lionello and @edwardrf for the .github/ directory
• Test files: @edwardrf, @edw-defang, and @lionello for the test/ directory

Benefits

• Automatic review assignment: When someone opens a pull request, the appropriate code owners will be automatically requested for review
• Clear responsibility: Makes it explicit who is responsible for maintaining different parts of the codebase
• Improved workflow: Streamlines the review process by ensuring the right people are notified about changes

The ownership assignments are based on the commit history analysis, identifying the primary contributors and maintainers for each area of the codebase.

Fixes #23.

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