These code changes propose using Django storage to store and serve
the Wagtail deletion archive from PR 8310 [0], instead of using Apache
to serve those files.

This simplifies the configuration and makes it easier to test locally
and easier to port in future to other webserver approaches.

With these changes, the deletion archive is now only available behind
the Wagtail admin login, at the URL /admin/__deleted/. This URL provides
a nicely formatted Wagtail report view where archives can be downloaded
(instead of the current PR approach that uses Apache directory serving).

With this change, Django storage configuration has been migrated to
settings.STORAGES from settings.STATICFILES_STORAGE, which was
deprecated in Django 4.2 and removed in Django 5.1.

Additionally, with this change, cf.gov deployments that have not defined
the WAGTAIL_DELETION_ARCHIVE_PATH environment variable still support
importing archives; the archive-on-delete and archive download
functionality is still disabled in those cases.

This commit also includes a minor bugfix to the archive import template
which doesn't currently properly display the destination page title.

[0] #8310