Add Publish to GitHub Packages workflow

[Copilot]

This PR adds a GitHub Actions workflow to automatically publish the json5-kotlin library to GitHub Packages.

Changes Made

• Added .github/workflows/publish-github-packages.yml workflow file

Workflow Features

Triggers:

• Automatic: On version tags (e.g., v1.0.0, v2.1.3)
• Manual: Via workflow_dispatch from GitHub Actions UI

Configuration:

• Uses Java 21 (matches project requirements from buildSrc)
• Caches Gradle packages for faster builds
• Uses GITHUB_TOKEN with github.actor for authentication
• Comprehensive inline comments explaining setup requirements

Key Benefits

• Zero additional setup required - leverages existing maven-publish configuration in lib/build.gradle.kts
• Secure authentication - uses GitHub's built-in GITHUB_TOKEN
• Flexible triggering - supports both automated tag-based and manual publishing
• Well-documented - extensive comments explain configuration options and alternatives

Usage

The workflow will automatically publish hossain.dev:json5kt:1.0.0 to GitHub Packages when:

1. A version tag is pushed (e.g., git tag v1.0.0 && git push origin v1.0.0)
2. Manually triggered from the GitHub Actions tab

Technical Notes

The existing publishing configuration in lib/build.gradle.kts already includes:

• Maven publication setup with proper metadata
• GitHub Packages repository configuration
• Authentication using USERNAME and TOKEN environment variables

This workflow simply provides the CI/CD automation layer on top of the existing setup.

Fixes #19.

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