Update ephemeral setup.py used by `dependency_utils.build_ephemeral_package()` to use `setuptools.find_namespace_packages()`.
Update ephemeral setup.py used by `dependency_utils.build_ephemeral_package()` to use `setuptools.find_namespace_packages()`.

This change is needed to correctly include the multiple package namespaces now covered by the `ml-pipelines-sdk` and `tfx` packages.

PiperOrigin-RevId: 345978142

tensorflow/tfx,tensorflow/tfx