Upgrade to Django 4.2 LTS

[int-y1]

Extended support for Django 3.2 is ending in April 2024.

#1649 is back.

[Ninjaclasher]

Things to do:

• Run https://github.com/adamchainz/django-upgrade
• s/ugettext_lazy/gettext_lazy, s/ifequal/if https://github.com/DMOJ/dmoj-wpadmin
• Bump https://github.com/etianen/django-reversion (quick testing suggests 5.0 works without any changes)
• (Hard) Fix https://github.com/DMOJ/online-judge/blob/master/judge/utils/raw_sql.py

[Ninjaclasher]

Remaining tasks:

• Fix django-pagedown
• Re-do all changes in https://github.com/DMOJ/martor with upstream.
• Fix django-select2