[predictor] aspect ratio true by default

[felixdittrich92]

This PR:

• change keeping the aspect ratio by default to True which will especially on images which are smaller as the default 1024x1024 improve the results

Any feedback is welcome 🤗

Ref.: #330 (already discussed with @charlesmindee)

[odulcy-mindee]

Fine to modify the default value

[codecov]

Codecov Report

Merging #1279 (95c7286) into main (95857cf) will increase coverage by 0.01%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1279      +/-   ##
==========================================
+ Coverage   95.75%   95.76%   +0.01%     
==========================================
  Files         154      154              
  Lines        6903     6903              
==========================================
+ Hits         6610     6611       +1     
+ Misses        293      292       -1     

Flag	Coverage Δ
unittests	95.76% <ø> (+0.01%)	⬆️

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

Files Changed	Coverage Δ
doctr/models/kie_predictor/pytorch.py	100.00% <ø> (ø)
doctr/models/kie_predictor/tensorflow.py	100.00% <ø> (ø)
doctr/models/predictor/pytorch.py	100.00% <ø> (ø)
doctr/models/predictor/tensorflow.py	100.00% <ø> (ø)
doctr/models/zoo.py	100.00% <ø> (ø)

... and 2 files with indirect coverage changes

[odulcy-mindee]

Thank you very much ! 🚀