[Feat] Add ActiveLearning Loop Customization v2

[tchaton]

What does this PR do?

This PR integrates Baal within Flash to offer ActiveLearning Training.

Fixes #761

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[codecov]

Codecov Report

Merging #779 (0aa0c97) into master (81b73ad) will decrease coverage by 2.14%.
The diff coverage is 42.66%.

@@            Coverage Diff             @@
##           master     #779      +/-   ##
==========================================
- Coverage   87.16%   85.02%   -2.15%     
==========================================
  Files         213      217       +4     
  Lines       11405    11623     +218     
==========================================
- Hits         9941     9882      -59     
- Misses       1464     1741     +277     

Flag	Coverage Δ
unittests	85.02% <42.66%> (-2.15%)	⬇️

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

Impacted Files	Coverage Δ
flash/core/data/data_module.py	94.50% <ø> (ø)
...ash/image/classification/integrations/baal/loop.py	34.83% <34.83%> (ø)
...ash/image/classification/integrations/baal/data.py	40.86% <40.86%> (ø)
.../image/classification/integrations/baal/dropout.py	45.00% <45.00%> (ø)
flash/core/trainer.py	84.12% <92.30%> (+0.94%)	⬆️
flash/core/utilities/imports.py	90.76% <100.00%> (+0.07%)	⬆️
...image/classification/integrations/baal/__init__.py	100.00% <100.00%> (ø)
flash/text/question_answering/model.py	29.16% <0.00%> (-61.81%)	⬇️
flash/text/question_answering/data.py	28.29% <0.00%> (-58.53%)	⬇️
flash/text/classification/cli.py	53.84% <0.00%> (-46.16%)	⬇️
... and 27 more

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[ethanwharris]

Looks good, could we have some documentation?

[pietrolesci]

I left some comments regarding the test dataset in the ActiveLearningDataModule

[SeanNaren]

Crushing it @tchaton!

[ethanwharris]

LGTM

[pietrolesci]

LGTM

Great work @tchaton!

[tchaton]

LGTM

Great work @tchaton!

Thanks @pietrolesci for helping understand what was required :) Great team work !

Next step, let's reproduce the result from Baal, LabelStudio integration.

Best,
T.C