Add Docker as an installation method

[vertti]

This PR adds Docker containerization for lazy-ecs to enable using with zero deps or installation

Docker Support

• Dockerfile: Multi-stage build using Python 3.13-slim for a minimal, secure image
• Automated Publishing: GitHub Actions workflow to build and push multi-platform images (linux/amd64, linux/arm64) to Docker Hub on releases
• Smart Entrypoint: Automatically handles AWS credential detection and region normalization
• Security: Runs as non-root user (lazyecs) for better container security

Enhanced Distribution

• Multiple Installation Options: Now supports Homebrew, pipx, Docker, and source installation