[timeseries] Update M5Forecast dataset and its unittest

[frankfliu]

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]

Codecov Report

Base: 72.08% // Head: 70.22% // Decreases project coverage by -1.86% ⚠️

Coverage data is based on head (8ca0b1c) compared to base (bb5073f).
Patch coverage: 71.57% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2105      +/-   ##
============================================
- Coverage     72.08%   70.22%   -1.87%     
- Complexity     5126     6119     +993     
============================================
  Files           473      612     +139     
  Lines         21970    27173    +5203     
  Branches       2351     2946     +595     
============================================
+ Hits          15838    19081    +3243     
- Misses         4925     6671    +1746     
- Partials       1207     1421     +214     

Impacted Files	Coverage Δ
api/src/main/java/ai/djl/modality/cv/Image.java	69.23% <ø> (-4.11%)	⬇️
...rc/main/java/ai/djl/modality/cv/MultiBoxPrior.java	76.00% <ø> (ø)
...rc/main/java/ai/djl/modality/cv/output/Joints.java	71.42% <ø> (ø)
.../main/java/ai/djl/modality/cv/output/Landmark.java	100.00% <ø> (ø)
...main/java/ai/djl/modality/cv/output/Rectangle.java	72.41% <0.00%> (ø)
...i/djl/modality/cv/translator/BigGANTranslator.java	21.42% <0.00%> (-5.24%)	⬇️
.../modality/cv/translator/ImageFeatureExtractor.java	0.00% <0.00%> (ø)
.../ai/djl/modality/cv/translator/YoloTranslator.java	27.77% <0.00%> (+18.95%)	⬆️
...modality/cv/translator/wrapper/FileTranslator.java	44.44% <ø> (ø)
...y/cv/translator/wrapper/InputStreamTranslator.java	44.44% <ø> (ø)
... and 535 more

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[zachgk]

One suggestion. Otherwise, LGTM

[zachgk]

Maybe we should keep this in S3/metadata instead

[frankfliu]

I think it's better keep it with the code:

1. This is tightly coupled with the code.
2. The s3 location become confusing, it doesn't make sense to keep it in unittest dataset
3. Users has to copy this file if they want to download dataset from Kaggle