Have lint run on __init__.py files

[angela97lin]

Closes #737 by adding configuration to ignore F401 (module imported but unused) on __init__.py files.

[codecov]

Codecov Report

Merging #1234 into main will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1234   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files         196      196           
  Lines       12206    12206           
=======================================
  Hits        12197    12197           
  Misses          9        9           

Impacted Files	Coverage Δ
evalml/automl/__init__.py	100.00% <ø> (ø)
evalml/automl/automl_algorithm/__init__.py	100.00% <ø> (ø)
evalml/automl/data_splitters/__init__.py	100.00% <ø> (ø)
evalml/data_checks/__init__.py	100.00% <ø> (ø)
evalml/demos/__init__.py	100.00% <ø> (ø)
evalml/model_family/__init__.py	100.00% <ø> (ø)
evalml/model_understanding/__init__.py	100.00% <ø> (ø)
..._understanding/prediction_explanations/__init__.py	100.00% <ø> (ø)
evalml/objectives/__init__.py	100.00% <ø> (ø)
evalml/pipelines/__init__.py	100.00% <ø> (ø)
... and 19 more

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[jeremyliweishih]

very cool!