Trac #31366: docbuild: switch from optparse to argparse

Sage's docbuilding uses [https://docs.python.org/3/library/optparse.html
optparse] for argument parsing, but this library has been deprecated for
a while. We should switch to
[https://docs.python.org/3/library/argparse.html argparse].

Some instructions for conversions can be found here:
https://docs.python.org/3/library/argparse.html#help

URL: https://trac.sagemath.org/31366
Reported by: jhpalmieri
Ticket author(s): Frédéric Chapoton
Reviewer(s): John Palmieri