Django: Upgrade to 4.2

[jpmckinney]

4.2 is the new LTS https://docs.djangoproject.com/en/4.2/releases/4.2/

• [ ] cove-oc4ids
• [ ] cove-ocds
• [x] data-registry
• [x] kingfisher-process
• [x] pelican-frontend
• [x] cookiecutter
• [x] spoonbill-web

Things to update:

• dj-database-url and django-* packages
• BASE_DIR STATIC_URL USE_L10N https://github.com/open-contracting/software-development-handbook/commit/f7331445ecf89095e8ffa9d0db873c74ade83081
• Kingfisher Process: https://docs.djangoproject.com/en/4.2/releases/4.1/#validation-of-constraints
• Can tidy https://docs.djangoproject.com/en/(?!4\.2) URLs in comments and documentation.
• Can upgrade to Python 3.11 (if running in Docker). See some upgrade notes at https://github.com/open-contracting/software-development-handbook/issues/11#issuecomment-713232896
• Run ./manage.py migrate and env PYTHONWARNINGS=error ./manage.py test

[jpmckinney]

Created follow-up issues for lower-priority Django projects.