Add callback parameter for explain_predictions_best_worst

[angela97lin]

Closes #2305

[codecov]

Codecov Report

Merging #2308 (9310394) into main (e323993) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main   #2308     +/-   ##
=======================================
+ Coverage   99.9%   99.9%   +0.1%     
=======================================
  Files        281     281             
  Lines      24566   24606     +40     
=======================================
+ Hits       24538   24578     +40     
  Misses        28      28             

Impacted Files	Coverage Δ
...nderstanding/prediction_explanations/explainers.py	100.0% <100.0%> (ø)
...s/prediction_explanations_tests/test_explainers.py	100.0% <100.0%> (ø)

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[jeremyliweishih]

lgtm once tests pass. Nice!

[chukarsten]

Awesome, very cool!