Add Label Encoder to LightGBM

[bchen1116]

Fix #1109

Add label Encoder for Binary classification case for LightGBM.

[codecov]

Codecov Report

Merging #1152 into main will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1152   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files         195      195           
  Lines       11515    11554   +39     
=======================================
+ Hits        11505    11544   +39     
  Misses         10       10           

Impacted Files	Coverage Δ
...ents/estimators/classifiers/lightgbm_classifier.py	100.00% <100.00%> (ø)
...alml/tests/component_tests/test_lgbm_classifier.py	100.00% <100.00%> (ø)

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[bchen1116]

Changed implementation to encode the labels if they weren't int64, regardless of whether it is binary or multiclass. I had run into errors when trying to pass string labels for multiclass instance, and this change fixed it.

[jeremyliweishih]

Looks good @bchen1116 - just a couple small comments but nothing blocking.

[freddyaboulton]

@bchen1116 Looks good to me!