Add face detection CLI

[ethanwharris]

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #1170 (cd3a563) into master (3c84e94) will increase coverage by 0.67%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1170      +/-   ##
==========================================
+ Coverage   90.20%   90.88%   +0.67%     
==========================================
  Files         285      286       +1     
  Lines       12745    12758      +13     
==========================================
+ Hits        11497    11595      +98     
+ Misses       1248     1163      -85     

Flag	Coverage Δ
unittests	90.88% <100.00%> (+0.67%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flash/__main__.py	95.23% <ø> (ø)
...ash/image/classification/integrations/baal/loop.py	94.77% <ø> (ø)
flash/image/face_detection/model.py	91.89% <ø> (+56.75%)	⬆️
...ash/image/classification/integrations/baal/data.py	93.93% <100.00%> (+0.12%)	⬆️
flash/image/face_detection/cli.py	100.00% <100.00%> (ø)
flash/image/face_detection/output_transform.py	100.00% <100.00%> (+55.55%)	⬆️
flash/text/question_answering/model.py	92.71% <0.00%> (+0.66%)	⬆️
flash/image/face_detection/data.py	82.60% <0.00%> (+8.69%)	⬆️
flash/image/face_detection/input.py	100.00% <0.00%> (+14.28%)	⬆️
... and 4 more

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