feat: Backport cms 4.0.x - Django 3.2 with Python 3.8 & 3.9 support, including update tooling

[yakky]

Description

Merge code from #70 with updated develop

References

Fix #70

Checklist

• [x] I have read the contribution guide
• [x] Code lint checked via inv lint
• [x] changes file included (see docs)
• [x] Usage documentation added in case of new features
• [x] Tests added

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (support/4.0.x@3f099fc). Click here to learn what that means. The diff coverage is n/a.

@@               Coverage Diff                @@
##             support/4.0.x      #77   +/-   ##
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  Coverage                 ?   94.56%           
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  Files                    ?        9           
  Lines                    ?      184           
  Branches                 ?       22           
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  Hits                     ?      174           
  Misses                   ?        7           
  Partials                 ?        3           

Flag	Coverage Δ
unittests	94.56% <0.00%> (?)

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[coveralls]

Coverage increased (+96.2%) to 96.154% when pulling 7c3c42c31ffcc4eedc18516a1506d940744f70c2 on feature/issue-74-update-django-cms4 into 9846374d93514756cbafaab7cd8f923e4e53631f on support/4.0.x.

[yakky]

@Aiky30 can you review this port of #70? I have merged with latest update from develop to make sure the two branches don't drift apart

I'll make a release to divio cloud with the current state of this branch and a beta one after merge

[yakky]

Replaced by #83 which includes the whole set of django CMS 4 changes