Add GitHub Actions workflow to build and publish Docker image to GHCR

[dabc24]

Motivation

• Provide an automated CI workflow to build and publish multi-architecture Docker images to GitHub Container Registry when code is pushed to main, a v* tag is created, or triggered manually.
• Ensure consistent image metadata and caching to speed up builds and support reproducible tags.
• Centralize build logic in repository so images are produced and versioned alongside code changes.

Description

• Add a new GitHub Actions workflow file at .github/workflows/docker-publish.yml that triggers on push to main, tag pushes matching v*, and workflow_dispatch manual runs.
• Configure permissions and steps to checkout the repo, set up QEMU with docker/setup-qemu-action@v3, set up Buildx with docker/setup-buildx-action@v3, and log in to GHCR with docker/login-action@v3.
• Use docker/metadata-action@v5 to generate image tags and docker/build-push-action@v6 to build multi-platform images for linux/amd64,linux/arm64, push to ghcr.io/${{ github.repository }}, and use GitHub Actions cache with cache-from/cache-to settings.

Testing

• No automated tests were executed as part of this change; the workflow itself will run on pushes to main, on matching tags, or via manual dispatch in CI.

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Codex Task