Provide more information to users about ensembling behavior

[angela97lin]

Closes #1461

[codecov]

Codecov Report

Merging #1527 (e2e8c7b) into main (3698425) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##             main    #1527     +/-   ##
=========================================
+ Coverage   100.0%   100.0%   +0.1%     
=========================================
  Files         234      234             
  Lines       16773    16803     +30     
=========================================
+ Hits        16765    16795     +30     
  Misses          8        8             

Impacted Files	Coverage Δ
evalml/automl/automl_search.py	99.7% <100.0%> (+0.1%)	⬆️
evalml/tests/automl_tests/test_automl.py	100.0% <100.0%> (ø)

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[freddyaboulton]

@angela97lin Looks great! I have one minor comment about letting the user know when ensembling will run if they specify a large enough number of iterations instead of batches. I think we only tell them anything if the number of iterations is too small.

I think we should also add coverage for the "Ensembling will run every k batches." message. Maybe in test_max_batches_works ?

[bchen1116]

Looks good to me. I like the test @freddyaboulton pointed out. Left one small suggestion, but nothing blocking.