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>
Paweł Gronowski
41a1782b35