Chore/switch pip plugin reference to python

[djgoku]

Summary

Remove pip plugin and use Python plugin.

How was it tested?

devbox run lint
devbox run test
go mod tidy
devbox shell testing new python plugin (cp plugins/python.json plugins/plugin.json and add "include": ["path:./plugins/"], to devbox.json. Though this is the output I got (not the Poetry message):

devbox % ./dist/devbox shell                       
Info: Ensuring packages are installed.
✓ Computed the Devbox environment.
Starting a devbox shell...
Virtual environment directory doesn't exist. Creating new one...

Poetry could not find a pyproject.toml file in /Users/dj_goku/dev/github/djgoku/devbox or its parents

[Lagoja]

Made two small tweaks:

1. Updated the packages listed in the docs snippet
2. I found a bug in how the UV_PYTHON variable was set, I so I changed that as well