Add Class Imbalance data check to api docs

[bchen1116]

Add class Imbalance Data check to the api documentation

[codecov]

Codecov Report

Merging #1190 into main will increase coverage by 0.18%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1190      +/-   ##
==========================================
+ Coverage   99.74%   99.92%   +0.18%     
==========================================
  Files         196      196              
  Lines       11977    11978       +1     
==========================================
+ Hits        11946    11969      +23     
+ Misses         31        9      -22     

Impacted Files	Coverage Δ
evalml/data_checks/class_imbalance_data_check.py	100.00% <ø> (ø)
evalml/data_checks/__init__.py	100.00% <100.00%> (ø)
...lml/tests/model_understanding_tests/test_graphs.py	100.00% <0.00%> (+0.15%)	⬆️
evalml/automl/automl_search.py	99.58% <0.00%> (+0.41%)	⬆️
.../automl_tests/test_automl_search_classification.py	100.00% <0.00%> (+0.45%)	⬆️
evalml/tests/component_tests/test_components.py	100.00% <0.00%> (+0.69%)	⬆️
evalml/tests/pipeline_tests/test_pipelines.py	100.00% <0.00%> (+0.78%)	⬆️
...ests/automl_tests/test_automl_search_regression.py	100.00% <0.00%> (+1.06%)	⬆️
evalml/utils/gen_utils.py	99.02% <0.00%> (+1.94%)	⬆️
evalml/tests/component_tests/test_utils.py	100.00% <0.00%> (+3.57%)	⬆️
... and 1 more

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[jeremyliweishih]

LGTM: you can view here.

[angela97lin]

LGTM, but @bchen1116 can I make the suggestion that you update the docstring of the ClassImbalanceDataCheck to not start with "Classification problem," as to better match the other data checks?

[dsherry]

@bchen1116 looks good! Please use a slightly more descriptive PR title, like "Add class imbalance data check to API ref". It makes it easier to understand what's in the PR quickly, and to search through old PRs / the logs.