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