[api] Adds center fit image operation for Yolo

[frankfliu]

• [pytorch] Adds pad operator
• [api] Adds center fit image operation for Yolo

Description

Brief description of what this PR is about

• If this change is a backward incompatible change, why must this change be made?
• Interesting edge cases to note here

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 39.39394% with 40 lines in your changes missing coverage. Please review.

Project coverage is 58.28%. Comparing base (c4baffb) to head (b87cc7f).
Report is 68 commits behind head on master.

Files with missing lines	Patch %	Lines
...n/java/ai/djl/modality/cv/transform/CenterFit.java	21.05%	15 Missing ⚠️
...i/djl/modality/cv/translator/YoloV5Translator.java	47.36%	8 Missing and 2 partials ⚠️
...y/cv/translator/SingleShotDetectionTranslator.java	0.00%	1 Missing and 4 partials ⚠️
.../ai/djl/modality/cv/translator/YoloTranslator.java	0.00%	4 Missing ⚠️
...jl/modality/cv/translator/BaseImageTranslator.java	71.42%	1 Missing and 1 partial ⚠️
...i/src/main/java/ai/djl/ndarray/NDArrayAdapter.java	0.00%	1 Missing ⚠️
...e/src/main/java/ai/djl/mxnet/engine/MxNDArray.java	0.00%	1 Missing ⚠️
.../main/java/ai/djl/tensorflow/engine/TfNDArray.java	0.00%	1 Missing ⚠️
...rs/src/main/java/ai/djl/engine/rust/RsNDArray.java	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3425      +/-   ##
============================================
+ Coverage     58.25%   58.28%   +0.03%     
- Complexity     5737     5775      +38     
============================================
  Files           668      669       +1     
  Lines         32509    32654     +145     
  Branches       3439     3472      +33     
============================================
+ Hits          18937    19033      +96     
- Misses        12125    12163      +38     
- Partials       1447     1458      +11     

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