Add DataCheckAction class and DataCheckActionCode enum

[angela97lin]

Closes #1878

[codecov]

Codecov Report

Merging #1896 (f89cce1) into main (b80cd3e) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##             main    #1896     +/-   ##
=========================================
+ Coverage   100.0%   100.0%   +0.1%     
=========================================
  Files         263      266      +3     
  Lines       21299    21348     +49     
=========================================
+ Hits        21293    21342     +49     
  Misses          6        6             

Impacted Files	Coverage Δ
evalml/data_checks/__init__.py	100.0% <100.0%> (ø)
evalml/data_checks/data_check_action.py	100.0% <100.0%> (ø)
evalml/data_checks/data_check_action_code.py	100.0% <100.0%> (ø)
.../tests/data_checks_tests/test_data_check_action.py	100.0% <100.0%> (ø)

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[freddyaboulton]

@angela97lin I think this is great!

[bchen1116]

Looks good to me! I agree with Freddy's suggestions though, it would be nice to default to the empty dict and return the string for the user.