Drop support for Django 2.2 (EOL)

[ulgens]

Depends on #566

[codecov]

Codecov Report

Merging #567 (d85e03e) into master (0f5c994) will decrease coverage by 0.11%.
The diff coverage is n/a.

❗ Current head d85e03e differs from pull request most recent head 62a1991. Consider uploading reports for the commit 62a1991 to get more accurate results

@@            Coverage Diff             @@
##           master     #567      +/-   ##
==========================================
- Coverage   84.60%   84.48%   -0.12%     
==========================================
  Files          51       51              
  Lines        2059     2056       -3     
==========================================
- Hits         1742     1737       -5     
- Misses        317      319       +2     

Impacted Files	Coverage Δ
silk/__init__.py	60.00% <ø> (-15.00%)	⬇️
silk/model_factory.py	82.96% <0.00%> (-0.88%)	⬇️

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[albertyw]

I see code coverage has dropped but it's only as a result of deleting code.

[albertyw]

I landed this too soon. I'm going to revert this for the v4.4.0 and unrevert this for v5.0.0