Django 1.11 is End-of-Life since April 2020 thus switch the following ports
to Django 2.2 (which has LTS support until April 2022):
* www/py-django-auth-ldap
* www/py-django-cacheops
* www/py-django-filter
* www/py-django-prometheus
Adjust the required Python version as Django 2.2 needs at least Python 3.5+
and bump the PORTREVISION for package change.
Mark the related py-dj22-* port variants as DEPRECATED because they're
obsolete now. Don't set an expiration date yet as they're still used by
some consumers and a few more Django 1.11 ports need to be assigned to
Django 2.2 first.
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