[WIP] Training Strategies

[ethanwharris]

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #571 (001957f) into master (08b56dd) will decrease coverage by 7.52%.
The diff coverage is 87.80%.

@@            Coverage Diff             @@
##           master     #571      +/-   ##
==========================================
- Coverage   89.98%   82.46%   -7.53%     
==========================================
  Files         149      151       +2     
  Lines        8457     8484      +27     
==========================================
- Hits         7610     6996     -614     
- Misses        847     1488     +641     

Flag	Coverage Δ
unittests	82.46% <87.80%> (-7.53%)	⬇️

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

Impacted Files	Coverage Δ
flash/image/classification/strategy/supervised.py	86.20% <86.20%> (ø)
flash/image/classification/model.py	79.16% <87.50%> (+0.32%)	⬆️
flash/core/registry.py	94.82% <100.00%> (-1.73%)	⬇️
flash/image/classification/strategy/__init__.py	100.00% <100.00%> (ø)
flash/image/detection/data.py	31.29% <0.00%> (-64.13%)	⬇️
flash/image/detection/serialization.py	30.76% <0.00%> (-63.47%)	⬇️
flash/audio/speech_recognition/collate.py	51.61% <0.00%> (-48.39%)	⬇️
flash/image/classification/data.py	46.05% <0.00%> (-48.03%)	⬇️
flash/audio/speech_recognition/backbone.py	55.55% <0.00%> (-44.45%)	⬇️
flash/image/segmentation/data.py	47.84% <0.00%> (-42.11%)	⬇️
... and 28 more

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[ethanwharris]

Being addressed in #682 and #737