Add cross-platform support for Windows and macOS runners

[Copilot]

This PR implements cross-platform compatibility to resolve the "Container action is only supported on Linux" error when running on Windows runners.

Problem

Previously, this action used runs.using: docker which only works on Linux runners. Users trying to run the action on Windows or macOS runners would get:

Error: Container action is only supported on Linux

Solution

Changed the action from a Docker action to a composite action that uses docker run directly, enabling it to work on any runner with Docker installed.

Key Changes

• action.yml: Changed from docker to composite action type with proper environment variable mapping
• run.sh: New cross-platform wrapper script that:
  • Detects the operating system
  • Checks Docker availability with helpful error messages
  • Executes the same Docker image using docker run
  • Passes all environment variables and inputs correctly
  • Automatically pulls the image if not present locally
• README.md: Updated documentation highlighting cross-platform support and Windows setup requirements

Platform Support

• ✅ Linux runners: Fully supported (existing functionality preserved)
• ✅ Windows runners: Now supported with Docker Desktop/Rancher Desktop
• ✅ macOS runners: Now supported with Docker installed

Usage Example

jobs:
  commit-changes:
    runs-on: windows-latest  # Now works!
    steps:
      - name: Checkout
        uses: actions/checkout@v4
      
      - name: Commit changes
        uses: devops-infra/action-commit-push@master
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          commit_message: "Cross-platform commit from Windows"

Backward Compatibility

✅ Existing Linux workflows continue to work unchanged - same Docker image, same environment, same behavior.

Implementation Details

The solution maintains the exact same execution environment by:

• Using the identical Docker image (devopsinfra/action-commit-push:v0.10.0)
• Preserving all environment variables and volume mounts
• Keeping the same working directory (/github/workspace)
• Running the same entrypoint.sh script inside the container

The only difference is how the Docker container is invoked:

• Before: GitHub Actions handles Docker execution (Linux only)
• After: Wrapper script handles Docker execution (cross-platform)

Fixes #103.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.launchpad.net
  • Triggering command: /usr/bin/python3 /usr/bin/add-apt-repository ppa:git-core/ppa (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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