Run SDK Docker builds as the host user

[jspaetzel]

Summary

• SDK Docker builds bind-mount the checkout. On rootful Docker they ran as root, so generated files could not be replaced by a later git checkout.
• bin/docker-user-args keeps root:root on rootless Docker (container root is already the host user) and uses the host uid/gid on rootful Docker. bin/docker-run applies that to every SDK docker run.
• PHP, Node, Python, Ruby, Java, and .NET wrappers, run-build, and the sandbox scripts use it. Package caches are host directories under .docker so the non-root user can write them. bin/redoc-container still runs as root because nginx binds port 80 and does not write the checkout.

Test plan

• On rootful Docker, bin/docker-run -v "$PWD:/work" -w /work alpine touch probe creates a file owned by the host user
• ./generate-sdks -t php (and one other language) leaves the SDK tree writable by the developer
• Rootless Docker still builds (docker-user-args prints --user root:root)
• DOCKER_RUN_AS_ROOT=1 restores the old root behavior