Add ability to generate `nbdev_pypi` output without uploading to PyPi

Uploading the dist directory to PyPi in response to a new release using GH Actions is a common workflow.

Hence, having the ability to generate the dist directory without uploading it to PyPI would be useful.

While `nbdev_pypi` both creates and uploads, perhaps we could add a `nbdev_dist` command to address this?

Comienza rastreando el comando existente `nbdev_pypi` y cómo el flujo de trabajo de GH Actions gestiona el directorio `dist`. Define el alcance del comando independiente `nbdev_dist` y, después, verifica que genere la distribución sin subirla a PyPI, preservando el comportamiento de subida existente.

Escrito por el modelo de indexación a partir del texto del issue.