[api] add NDArray gammaln and sample distribution function support.

[Carkham]

Description

This PR implements several function.

gammaln is the same as the log gamma function of torch.lgamma, mxnet.nd.gammaln.
It is used in the distributions package of torch and mxnet to calculate the probability density at the value, and this result can be used for the loss function calculation of the predicting probability distribution model. This is the training process.

sample is the same as the sample distribution function of torch.distributions.Distribution.sample, mxnet.nd.sample_xxx
It is used in the ditributions package to draw samples from corresponding distribution. The samples serve as inference outputs of the model and can be converted to Forecast through TimeSeriesTranslator. This is the inference process.

I'm not sure which java class the sample_xxx function should be placed in. I put them in the NDManager for the time being, because these functions look similar to NDManager.random functions.

[codecov-commenter]

Codecov Report

Merging #1990 (9b0d039) into master (bb5073f) will decrease coverage by 2.19%.
The diff coverage is 67.99%.

@@             Coverage Diff              @@
##             master    #1990      +/-   ##
============================================
- Coverage     72.08%   69.89%   -2.20%     
- Complexity     5126     5929     +803     
============================================
  Files           473      586     +113     
  Lines         21970    26244    +4274     
  Branches       2351     2846     +495     
============================================
+ Hits          15838    18344    +2506     
- Misses         4925     6520    +1595     
- Partials       1207     1380     +173     

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%)	⬇️
...odality/cv/translator/BigGANTranslatorFactory.java	33.33% <0.00%> (+8.33%)	⬆️
.../cv/translator/InstanceSegmentationTranslator.java	0.00% <0.00%> (-86.59%)	⬇️
...nslator/InstanceSegmentationTranslatorFactory.java	7.14% <0.00%> (-11.04%)	⬇️
.../cv/translator/SemanticSegmentationTranslator.java	0.00% <0.00%> (ø)
... and 509 more

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