www/py-django22: Deprecate and set to expire

[kai]

Summary

Django 2.2 will reach its End-of-Life in April 2022.

Set the deprecation note and let it expire to the end of June to give enough time to switch all affected ports over to Django 3.2 which is the next LTS release.

PR: TBA

Test Plan

1. Create a meta bug to track the whole progress
2. Update as many ports during 2022Q1 but keep them assigned to Django 2.2
3. Once 2022Q2 is branched, switch all those ports to Django 3.2
4. Deprecate the py-dj32* ports as they are superfluous then
5. If everything goes well Django 2.2 should be ready to be deorbited to the end of June 2022
6. Plan B: Extend the deprecation date if some upstream repositories (e.g. Seahub) need a bit more time

See also: https://wiki.freebsd.org/Ports/Django/Django32Migration

[kai]

Reworded the deprecation note as suggested by @koobs .

[dbaio]

LGTM, it will give reasonable time for people to plan their Django upgrade.