feat: Added latency evaluation scripts for all tasks

[fg-mindee]

As per #699, some latency benchmarking was required. This PR introduces scripts in PyTorch & TensorFlow to benchmark latency on CPU & GPU for text recognition and text detection.

The results were added in a csv file in the same folder to keep track of latency changes for each model.

Finally, a CI job was added to ensure those scripts can run properly.

Any feedback is welcome!

[codecov]

Codecov Report

Merging #746 (8766582) into main (a1291f0) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #746      +/-   ##
==========================================
+ Coverage   96.07%   96.12%   +0.04%     
==========================================
  Files         129      129              
  Lines        4794     4794              
==========================================
+ Hits         4606     4608       +2     
+ Misses        188      186       -2     

Flag	Coverage Δ
unittests	96.12% <100.00%> (+0.04%)	⬆️

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Impacted Files	Coverage Δ
doctr/models/detection/linknet/tensorflow.py	100.00% <100.00%> (ø)
doctr/models/builder.py	99.12% <0.00%> (+1.75%)	⬆️

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[charlesmindee]

Thanks!