Upgrade to Django 5.2

[joemull]

Django 4.2 will reach end of LTS support in April 2026.

Django 5.2 has several benefits that we could use, including simpler templates for form rendering and the a template tag for query strings.

Django 5.2 release notes.

To do

• Check the backwards-incompatible changes for likely problems.
• Plan which version to upgrade on.
• Upgrade.