[docs] Move jupyter notebooks to DJL Demo

[zachgk]

This moves the notebooks to the demo repositories. It makes it more clearly follow the trend where the things in the main repo are master build while those in demos track nightly snapshots or releases.

Combined with deepjavalibrary/djl-demo#390

[lanking520]

we also have a job that just run those notebook and append output result, does that still work with this change?

[zachgk]

we also have a job that just run those notebook and append output result, does that still work with this change?

Are you referring to the docs action? I updated that one (and it won't pass until both changes are merged) so this PR is not expected to pass CI

[codecov-commenter]

Codecov Report

Attention: 1363 lines in your changes are missing coverage. Please review.

Comparison is base (bb5073f) 72.08% compared to head (c2388b0) 72.30%.
Report is 912 commits behind head on master.

Files	Patch %	Lines
...va/ai/djl/modality/nlp/generate/TextGenerator.java	2.81%	276 Missing ⚠️
.../java/ai/djl/modality/nlp/generate/SeqBatcher.java	0.75%	132 Missing ⚠️
...ity/nlp/generate/ContrastiveSeqBatchScheduler.java	2.97%	98 Missing ⚠️
...i/djl/modality/nlp/generate/SeqBatchScheduler.java	9.83%	55 Missing ⚠️
.../java/ai/djl/modality/cv/BufferedImageFactory.java	40.96%	47 Missing and 2 partials ⚠️
...a/ai/djl/modality/nlp/generate/StepGeneration.java	2.04%	48 Missing ⚠️
api/src/main/java/ai/djl/ndarray/NDArray.java	43.42%	39 Missing and 4 partials ⚠️
...n/java/ai/djl/modality/cv/output/CategoryMask.java	22.00%	39 Missing ⚠️
...i/src/main/java/ai/djl/ndarray/NDArrayAdapter.java	71.21%	31 Missing and 7 partials ⚠️
.../cv/translator/SemanticSegmentationTranslator.java	37.50%	35 Missing ⚠️
... and 76 more

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2854      +/-   ##
============================================
+ Coverage     72.08%   72.30%   +0.21%     
- Complexity     5126     7162    +2036     
============================================
  Files           473      708     +235     
  Lines         21970    31908    +9938     
  Branches       2351     3313     +962     
============================================
+ Hits          15838    23070    +7232     
- Misses         4925     7259    +2334     
- Partials       1207     1579     +372     

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