Add standard opencontainers labels to images

[pkwarren]

Update the Docker build to specify standard opencontainers labels on images using hte docker/metadata-action.

[pkwarren]

These look pretty handy to include:

    "labels": {
      "org.opencontainers.image.created": "2024-02-02T19:27:11.306Z",
      "org.opencontainers.image.description": "The best way of working with Protocol Buffers.",
      "org.opencontainers.image.licenses": "Apache-2.0",
      "org.opencontainers.image.revision": "e69a37dd230f113372f66db3a28d47f125da0865",
      "org.opencontainers.image.source": "https://github.com/bufbuild/buf",
      "org.opencontainers.image.title": "buf",
      "org.opencontainers.image.url": "https://github.com/bufbuild/buf",
      "org.opencontainers.image.version": "edge"
    }