Add the optional build-arg input

What's Changed

• Bump actions/checkout from 3 to 4 by @dependabot in #34
• Wrap "docker build" with set -x / set +x by @macbre in #35
• add ghcr badge by @ipitio in #40
• Add the optional build-arg input by @macbre in #41

New Contributors

• @ipitio made their first contribution in #40

Full Changelog: v13...v14