Upgrade to Wagtail 5.2 LTS

[phette23]

• read all interim release notes and highlight major changes here
• upgrade to latest Wagtail 4.2
  • feat: Accessibility Checker in Wagtail User bar
  • feat: users can choose between an inline or fixed position rich text toolbar
• upgrade to latest Wagtail 5.0
  • adds Django 4.2 support
  • feat: object information on delete
  • feat: SVG images are now supported
  • more complex StreamField validation available, see if this is useful to our LinkBlock
  • Editor minimap improvements: stays open until dismissed
  • feat: Admin side will be in Dark mode if that's your system setting
  • Numerous deprecated features removed but few should affect us
  • Elasticsearch backend no longer performs partial matching on search but we can be OK with that
• upgrade to latest Wagtail 5.1
  • adds Elasticsearch 8 support (also makes "boost" option work again)
  • AVIF image support
  • add AutoComplete fields to search indices
• upgrade to latest Wagtail 5.2
  • feat: redesigned page listing view
  • change MenuItem classnames to classname singular in libraries/home/wagtail_hooks.py
  • picture template tag, see if we have places for this
  • External links in search promotions may have uses, are there searches people make on Libraries that belong elsewhere?
  • adds Python 3.12 support
  • feat: subject and body fields in the Email link chooser form