ci(docker): Add Dockerfile and configure GitHub Actions

[HuckOps]

This PR adds support for containerizing the project and automated CI image building:


• Add a valid Dockerfile for building gogcli container image
• Configure GitHub Actions workflow to automatically build and push Docker images to GHCR on code update

[steipete]

Thanks for kicking this off. I landed Docker image support on main in d37caab, with a rewrite around the production bits: static Linux binary, non-root Alpine runtime, pinned Docker Actions, no go.mod mutation during image build, .dockerignore, README container/keyring docs, and changelog credit.\n\nLive proof before landing:\n- docker build --no-cache -t gogcli:docker-test-nocache .\n- docker run --rm gogcli:docker-test-nocache version\n- docker run with GOG_KEYRING_BACKEND=file + mounted config volume: auth list --json returned an empty account list and created the keyring directory\n- actionlint\n- make ci\n- GitHub CI for d37caab is green\n\nClosing this PR as superseded by the landed main commit. Thanks again!