[api] input property key should be case-insensitive

[frankfliu]

Change-Id: I9bcb5aab336f553f979b58523051af75ea134d90

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 #1264 (6f37fb8) into master (64e4b1b) will decrease coverage by 0.00%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master    #1264      +/-   ##
============================================
- Coverage     71.99%   71.98%   -0.01%     
  Complexity     5113     5113              
============================================
  Files           473      473              
  Lines         21909    21913       +4     
  Branches       2345     2345              
============================================
+ Hits          15774    15775       +1     
- Misses         4932     4933       +1     
- Partials       1203     1205       +2     

Impacted Files	Coverage Δ
api/src/main/java/ai/djl/inference/Predictor.java	91.34% <ø> (ø)
api/src/main/java/ai/djl/modality/Input.java	91.30% <66.66%> (-4.09%)	⬇️

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