add setuptools to dependencies

[xopham]

I believe guarddog technically depends on setuptools though that is installed in most cases. To test this:

1. Run a python container: docker run -it python /bin/bash
2. Create an environment with bare dependencies

   cd /home
   pip install poetry
   python -m venv venv --without-pip
   . venv/bin/activate
   poetry init --quiet
   poetry add guarddog
   deactivate

3. Activate virtual environment and convince yourself that you are running guarddog in venv

   guarddog  # fails because we are not in the venv
   . venv/bin/activate
   which guarddog
   guarddog

4. guarddog fails with lack of pkg_resources

That said, it might be possible to reduce installed part of setuptools as is done in pip