feat: Added Gaussian Noise implementation in Tensorflow

[SiddhantBahuguna]

This PR adds the following changes to the existing repo:

• It adds Gaussian Noise augmentation implementation in Tensorflow
• It adds a unittest for the same in Tensorflow
• Added GaussianNoise in the documentation

Any feedback is welcome!

[codecov]

Codecov Report

Merging #771 (867152d) into main (f5b6375) will decrease coverage by 0.01%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main     #771      +/-   ##
==========================================
- Coverage   95.93%   95.92%   -0.02%     
==========================================
  Files         129      129              
  Lines        4845     4857      +12     
==========================================
+ Hits         4648     4659      +11     
- Misses        197      198       +1     

Flag	Coverage Δ
unittests	95.92% <91.66%> (-0.02%)	⬇️

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Impacted Files	Coverage Δ
doctr/transforms/modules/tensorflow.py	92.42% <91.66%> (-0.08%)	⬇️
doctr/transforms/modules/base.py	94.52% <0.00%> (ø)

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[fg-mindee]

Looks good, thanks!