[example] add an example of time sereis model training

[Carkham]

Description

This is an example of how to use a time series model for training on real world data, we chose the dataset from https://www.kaggle.com/competitions/m5-forecasting-accuracy, which predicts for the unit sales of Walmart retail goods. We customize the corresponding metrics to evaluate the inference ability of the model.

Considering the performance of model training, we corase grain the datasets so that the predictions are measured per week, which eliminates the sparse zero sales. This achieves good results.

[codecov-commenter]

Codecov Report

Base: 72.08% // Head: 67.88% // Decreases project coverage by -4.20% :warning:

Coverage data is based on head (1b50d1c) compared to base (bb5073f). Patch coverage: 68.25% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2031      +/-   ##
============================================
- Coverage     72.08%   67.88%   -4.21%     
- Complexity     5126     5960     +834     
============================================
  Files           473      612     +139     
  Lines         21970    27173    +5203     
  Branches       2351     2942     +591     
============================================
+ Hits          15838    18446    +2608     
- Misses         4925     7342    +2417     
- Partials       1207     1385     +178     

Impacted Files	Coverage Δ
api/src/main/java/ai/djl/modality/cv/Image.java	69.23% <ø> (-4.11%)	:arrow_down:
...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%)	:arrow_down:
...odality/cv/translator/BigGANTranslatorFactory.java	33.33% <0.00%> (+8.33%)	:arrow_up:
.../cv/translator/InstanceSegmentationTranslator.java	0.00% <0.00%> (-86.59%)	:arrow_down:
...nslator/InstanceSegmentationTranslatorFactory.java	7.14% <0.00%> (-11.04%)	:arrow_down:
.../cv/translator/SemanticSegmentationTranslator.java	0.00% <0.00%> (ø)
... and 525 more

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