gh-90300: Improve the Python CLI help output (GH-115853)

* document equivalent command-line options for all environment variables
* document equivalent environment variables for all command-line options
* reduce the size of variable and option descriptions to minimum
* remove the ending period in single-sentence descriptions

Co-authored-by: Éric <merwok@netwok.org>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>