This is needed to work with having namespace packages disabled.
`sardine.cli.main` will still exist, but the preferred entrypoint
should be `sardine.cli` or `sardine-config`.

- Adds setup.py with build subcommand to run yarn build
- Excludes .svelte-kit and build artifacts from sdist
- Disables include_package_data for setuptools
  This makes MANIFEST.in only apply to the source distribution,
  which is necessary to avoid including the fishery client's source.
  As a consequence, data files must be explicitly listed in pyproject.toml.

Actually might be a better idea to explicitly upgrade dependencies
than to grab the latest compatible versions each time