bpo-37860: Add netlify deploy preview for docs (GH-15288)

* add netlify deploy preview

* fix publish path

* install python3 venv

* add sudo

* try without venv

* install right dependencies

* use python3, not python

* use pip3

* python3.7

* use requirements.txt

* move requirements.txt to Doc

* use python 3.7 in runtime.txt

* move runtime.txt

* Update requirements.txt