[ort] Add support for registerCustomOpLibrary.

[frankfliu]

Change-Id: Ic3ec4249adb432b2a54668b7a45481698fa83ea5

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

Merging #1771 (370d351) into master (bb5073f) will decrease coverage by 1.41%.
The diff coverage is 70.76%.

@@             Coverage Diff              @@
##             master    #1771      +/-   ##
============================================
- Coverage     72.08%   70.67%   -1.42%     
- Complexity     5126     5575     +449     
============================================
  Files           473      527      +54     
  Lines         21970    24740    +2770     
  Branches       2351     2682     +331     
============================================
+ Hits          15838    17485    +1647     
- Misses         4925     5924     +999     
- Partials       1207     1331     +124     

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% <ø> (-5.24%)	⬇️
...odality/cv/translator/BigGANTranslatorFactory.java	33.33% <0.00%> (+8.33%)	⬆️
...nslator/InstanceSegmentationTranslatorFactory.java	14.28% <0.00%> (-3.90%)	⬇️
.../cv/translator/StyleTransferTranslatorFactory.java	40.00% <ø> (ø)
.../ai/djl/modality/cv/translator/YoloTranslator.java	8.33% <0.00%> (-0.50%)	⬇️
... and 411 more

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[zachgk]

Should we document this option somewhere?