Python: Limit registered language runtimes to Python 3.8+

[petetronic]

Python 3.7 is very close to EOL, and a key module we rely on for our functionality, ipykernel, now reports that it requires >= 3.8. We should filter out Python interpreters we find that are less than 3.8 and not register them with the jupyter-adapter.

[petetronic]

Thanks Wasim, this is now implemented. I had earlier Python's installed, including 3.6 and 3.7, and our language runtime selector does not offer them as an option. The earliest it offers is 3.8.