Implement the Initial Version of the Gemini CLI GitHub Action

[jerop]

The current GitHub Action in this repository is a non-functional placeholder based on the default Node.js template. This task involves replacing the placeholder with a fully-featured, composite GitHub Action that installs and runs the gemini CLI, enabling users to integrate Gemini CLI directly into their workflows. This involves mostly migrating the prototype from https://github.com/google-gemini/gemini-cli-action with some modifications.

Acceptance Criteria:

• Action Implementation:

  • The action must be converted from a Node.js action to a composite action.
  • The action.yml file must be created with the necessary inputs to configure and run the gemini CLI.
  • The action must handle the installation of the gemini CLI on the runner.

• Documentation:

  • Create a comprehensive README.md with clear usage instructions, input descriptions, and examples.
  • Add detailed documentation in the docs/ directory
    covering:
    • Authentication (GitHub Apps and Workload Identity Federation).
    • Observability and Telemetry setup.
    • Step-by-step guides for core use cases (e.g., issue triage, PR review).

• Example Workflows:

  • Provide ready-to-use example workflow files in the examples/ directory for:
    • Automated issue triage.
    • Scheduled issue triage.
    • Pull request review.

• Helper Scripts:

  • Include a script to help users set up Google Cloud Workload Identity Federation.

• Project Cleanup:

  • Remove all placeholder Node.js files (package.json, src/, tests/, tsconfig.json, etc.).
  • Update .gitignore and other configuration files to match the new project structure.