Add disk space monitoring and cleanup to Docker build workflow

[neubig]

This PR adds disk space monitoring and cleanup steps to the Docker build workflow to help prevent disk space issues.

Changes:

• Add disk space monitoring before build, after build, and after hash verification
• Add Docker cleanup steps to free up space after major operations
• Monitor largest files and directories to identify space usage
• Use docker system prune and builder prune to clean up unused resources

This should help prevent disk space issues like the one seen in #6346.

Note: This is a simplified version of #6627 that only modifies the ghcr-build.yml file.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:251184d-nikolaik   --name openhands-app-251184d   docker.all-hands.dev/all-hands-ai/openhands:251184d