Replace `pip` with `pipenv`

[nikola-rados]

Pipenv is the new standard installation tool recommended by python. For this issue we want to replace all instances of pip with pipenv. There are several places that you will need to consider:

• Makefiles
• github workflows
• Dockerfiles
• setup.py
• READMEs

A few other tips:

• when installing packages used in test_requirements.txt use pipenv install --dev -r test_requirements.txt to install them to the dev-packages space
• many of the environment variables and target used in Makefiles will no longer be required
• ensure *.lock files are not included in the .gitignore

Happy updating!