Publish devcontainer as Docker image for reuse in other projects

[lanrat]

Thanks for creating this excellent Pebble development devcontainer. It would be really helpful if this devcontainer could be published as a Docker image to GitHub Container Registry (GHCR) so that other Pebble projects can easily extend and inherit from it.

Publishing as an image would allow projects to reference it directly in their devcontainer.json using the "image" field, automatically inheriting updates without duplicating configuration.

This could be achieved with a GitHub Action that builds and publishes the image on commits to main or on releases.