Add opt-in `sandbox.docker.gpus` config plumbing for Docker sandbox containers.
- thread the optional GPU passthrough field through config types, schema, resolution, and Docker create args
- reject empty config values and emit `--gpus` as a separate Docker argv pair
- document the Docker-only behavior and credit the original contributor in the changelog
Fixes#57976.
Carries forward #58124 from @cyan-ember.
Co-authored-by: cyan-ember <5855097+cyan-ember@users.noreply.github.com>