Automate container build and push via GitHub Actions

[chicks-net]

Current State

Container building and publishing is currently a manual process using just commands:

• just build_con - Build container with Podman
• just ghcr_push - Push container to GitHub Container Registry

Proposal

Move container generation into a GitHub Action to automate the build and publish workflow.

Benefits

• Automation: No manual intervention needed for container updates
• Consistency: Every commit/release gets a tested, reproducible container build
• CI/CD Integration: Leverage existing GitHub Actions infrastructure (already used for markdown linting and Checkov scanning)
• Version Tagging: Automatic tagging based on git refs (commit SHA, branch, tags)

Implementation Notes

• Should build on push to main and on release tags
• Consider multi-arch builds (amd64, arm64) if needed
• Use GitHub's built-in GHCR authentication
• May need to handle both Podman and Docker builders in the action
• Could add a matrix build strategy for different CoreDNS versions

Related Files

• Container_root/Corefile - CoreDNS configuration
• Containerfile - Container definition
• .just/gh-process.just - Current justfile automation