SSH Support + Gerrit repos

[renan-alm]

This pull request introduces major improvements to authentication flexibility, platform support, and documentation for the repository sync GitHub Action. Notably, it adds comprehensive SSH and Gerrit support, allows separate credentials for source and destination repositories, and updates documentation and configuration files to reflect these enhancements.

Authentication enhancements:

• Added support for SSH authentication, including options for providing SSH keys directly, via file path, with passphrases, and custom known hosts. The action now supports mixed HTTPS and SSH authentication in a single workflow and automatic detection based on repository URL. (README.md, action.yml) [1] [2]
• Introduced separate source_token and destination_token inputs, enabling the use of different credentials for source and destination repositories, which is essential for cross-platform or cross-organization syncs. (README.md, action.yml) [1] [2]

Platform support improvements:

• Added automatic detection and support for Gerrit repositories, including documentation on Gerrit workflows, authentication, and troubleshooting. The action now pushes to Gerrit review queues using refs/for/* when appropriate. (GERRIT_SUPPORT.md, action.yml) [1] [2]

Documentation and usage examples:

• Expanded and clarified documentation with new usage examples for SSH, mixed authentication, and separate tokens. Added detailed instructions for SSH key management and host key configuration. (README.md) [1] [2]
• Updated the main action description and input documentation to reflect new features and supported platforms. (action.yml) [1] [2]

Configuration and code quality:

• Added a Prettier configuration file for consistent code formatting. (.prettierrc.json)
• Updated package.json to use dist/index.js as the entry point and improved build/lint scripts for better maintainability. (package.json)

Copilot and contributor guidelines:

• Added explicit rules for GitHub Copilot in the project documentation. (.github/copilot-instructions.md)