Resolve #194 -- Add support to run Pictures for a image CDN

[codingjoe]

Add support documented support to run an external image processor like Cloudinary or AWS lambda.

This does not remove the need to have Pillow installed, as Django requires Pillow to read the image dimensions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (9ebc0f6) to head (8573caa).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #195   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           13        13           
  Lines          489       496    +7     
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+ Hits           489       496    +7     

Flag	Coverage Δ
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cleanup	88.50% <89.47%> (+0.16%)	⬆️
dj4.1	88.50% <89.47%> (+0.16%)	⬆️
dj4.2	88.50% <89.47%> (+0.16%)	⬆️
django-rq	85.08% <89.47%> (+0.21%)	⬆️
dramatiq	85.08% <89.47%> (+0.21%)	⬆️
drf	96.37% <100.00%> (+0.05%)	⬆️
macos-latest	88.70% <89.47%> (+0.16%)	⬆️
py3.10	88.50% <89.47%> (+0.16%)	⬆️
py3.12	88.50% <89.47%> (+0.16%)	⬆️
py3.8	88.50% <89.47%> (+0.16%)	⬆️
py3.9	88.50% <89.47%> (+0.16%)	⬆️
ubuntu-latest	88.50% <89.47%> (+0.16%)	⬆️
windows-latest	81.76% <33.33%> (+0.05%)	⬆️

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[herrbenesch]

@codingjoe
I cannot really tell how the changes allow hosting on a CDN. I'll need to trust you on this.
Nevertheless, I left you some comments targeted at documentation.