Less invasively detect presence of installed setuptools and wheel.

[jaraco]

Also includes a refactor to avoid interacting booleans and rewriting variables and using argparse for parsing out known args.

[pradyunsg]

You need to modify the templates: https://github.com/pypa/get-pip/blob/main/templates/default.py

Running nox -s generate after modifying the templates will create the scripts correctly.