Automatically set `unpack=false` for registry exports unless explicitly overridden by the user. This applies to: - `registry` exporter type (converted to `image` exporter with `push=true`) - `--push` flag usage with image exporters Users can still explicitly set `unpack=true` if they need local image storage alongside registry push. Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>