Define what Python, Django and DRF series are supported

[sliverc]

Description of the Change

Currently whenever a Python, Django and Django REST framework series is end of life there is a conversation on when to drop it. I think for a user of DJA it is good to have this defined to avoid surprises.

Django REST framework does not really have an end of life definition (or have I overlooked this?) so supporting the last two series is feasible. In our upcoming release 4.0.0 we actually started supporting a new DRF release and dropping all lower DRF versions. Therefore a user is forced to update DJA and DRF at the same time.

I think it is fine for this round but should be avoided this in the future.

This PR should be the basis of discussion and can also be merged after the release of 4.0.0 whatever fits best.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #839 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #839   +/-   ##
=======================================
  Coverage   97.76%   97.76%           
=======================================
  Files          58       58           
  Lines        3089     3089           
=======================================
  Hits         3020     3020           
  Misses         69       69           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ab3fbfc...360dcb2. Read the comment docs.