Python data science walkthrough version 2

[luabud]

Option 1 – ship only the “Python” and “Jupyter” walkthroughs with each extension (merge contents from “Python DS” into these)
Option 2 – ship the “Python DS” with both extensions, but ship it nestled under the primary walkthroughs for each extension (i.e. “Python DS” is only accessible via a link from the “Python” walkthrough for the Python extension, and as a link from the “Jupyter” walkthrough for the Jupyter extension)

[luabud]

Closed by #18321.