Move the management of `sphinx` related PyPI deps to that `MODULE.bazel`. Currently `dev_pip` hub repo has more than is needed by the docs only, I think.

[aignas]

[rickeylev]

This requires the pip.dep() functionality we've talked about previously.

The basic problem there's no good way to have the sphinxdocs rule integrate with the caller's dependency closure.

[aignas]

I am not sure, sphinx is a tool that should be versioned separately from the rest of the pythontools. Similar to howwehave twine in rules_python.

We could go the way that you suggest, but that is one of the options and not the only one.