feat: Added Random Horizontal Flip augmentation

[SiddhantBahuguna]

This PR introduces the following changes:

• It adds Random horizontal Flip as an augmentation that transforms images as well as the labels.

       from doctr.transforms import RandHorizontalFlip
       import torch; import numpy as np
       transformed = RandHorizontalFlip(p = 0.5)
       target = {"boxes": np.array([[0.1, 0.1, 0.4, 0.5] ], dtype= np.float32), "labels": np.ones(1, dtype= np.int64)}
       image, target = transformed(torch.rand((3, 224, 224)), target)
  

• It adds a uniitest for the same

Any feedback is welcome!

[codecov]

Codecov Report

Merging #773 (150fb25) into main (f5b6375) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 150fb25 differs from pull request most recent head 2142583. Consider uploading reports for the commit 2142583 to get more accurate results

@@            Coverage Diff             @@
##             main     #773      +/-   ##
==========================================
- Coverage   95.93%   95.93%   -0.01%     
==========================================
  Files         129      129              
  Lines        4845     4866      +21     
==========================================
+ Hits         4648     4668      +20     
- Misses        197      198       +1     

Flag	Coverage Δ
unittests	95.93% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
doctr/transforms/modules/pytorch.py	98.30% <100.00%> (+0.30%)	⬆️
doctr/transforms/modules/tensorflow.py	92.42% <0.00%> (-0.08%)	⬇️

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[fg-mindee]

Thanks!