chore: Upgrade to Django 3.2

[jennifer-richards]

A couple changes of note:

• Drops stale package django-password-strength. The BSD-licensed code for the widgets are moved to ietfauth.widgets. We were already using a copy of the JS code in our password_strength.js
• requirements.txt now includes a bunch of types-* python packages for mypy tests - I haven't looked into installing these only for testing

[codecov]

Codecov Report

Merging #5629 (b714bfb) into feat/django4 (d0cb46d) will decrease coverage by 0.01%.
The diff coverage is 91.93%.

@@               Coverage Diff                @@
##           feat/django4    #5629      +/-   ##
================================================
- Coverage         88.73%   88.73%   -0.01%     
================================================
  Files               285      287       +2     
  Lines             39812    39841      +29     
================================================
+ Hits              35328    35353      +25     
- Misses             4484     4488       +4     

Impacted Files	Coverage Δ
ietf/doc/views_stats.py	74.80% <ø> (-0.20%)	⬇️
ietf/doc/views_review.py	94.97% <83.33%> (+<0.01%)	⬆️
ietf/ietfauth/widgets.py	84.61% <84.61%> (ø)
ietf/api/serializer.py	76.02% <100.00%> (ø)
ietf/api/urls.py	100.00% <100.00%> (ø)
ietf/community/views.py	97.59% <100.00%> (+0.01%)	⬆️
ietf/doc/urls.py	100.00% <100.00%> (ø)
ietf/group/urls.py	100.00% <100.00%> (ø)
ietf/ietfauth/forms.py	95.32% <100.00%> (ø)
ietf/ietfauth/utils.py	92.81% <100.00%> (ø)
... and 11 more

... and 2 files with indirect coverage changes