Add Target Encoder to Components

[bchen1116]

fix #1390

Adding target encoder to components. Perf test results are here

Docs are here

[UPDATE]
On Friday, 11/6, we decided to add additional perf tests for TE (discussion in the quip doc above).
Things to test:

1. Running OHE vs TE on categorical string data
2. Running OHE vs TE on categorical data that has already been converted to int/float
3. Running OHE vs TE on categorical data that has already been converted to int/float, where we convert the column type to categorical if there are less than 10 unique values in that column.

The perf test doc contains these 3 tests, ordered from 3, 1, 2.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #1401 (2e3b007) into main (c470196) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##             main    #1401     +/-   ##
=========================================
+ Coverage   100.0%   100.0%   +0.1%     
=========================================
  Files         218      220      +2     
  Lines       14433    14582    +149     
=========================================
+ Hits        14426    14575    +149     
  Misses          7        7             

Impacted Files	Coverage Δ
evalml/pipelines/__init__.py	100.0% <ø> (ø)
evalml/pipelines/components/__init__.py	100.0% <ø> (ø)
evalml/pipelines/pipeline_base.py	100.0% <ø> (ø)
...alml/pipelines/components/transformers/__init__.py	100.0% <100.0%> (ø)
...lines/components/transformers/encoders/__init__.py	100.0% <100.0%> (ø)
...components/transformers/encoders/target_encoder.py	100.0% <100.0%> (ø)
...valml/tests/component_tests/test_target_encoder.py	100.0% <100.0%> (ø)
evalml/tests/component_tests/test_utils.py	100.0% <100.0%> (ø)

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[freddyaboulton]

@bchen1116 Looks good! Thanks for hunting down that weird bug hehe. I have a suggestion for how to guard against that bug without taking the extreme measure of resetting the index at the pipeline level. But maybe that is something we should consider in the future! Custom indices have shot us in the foot so many times lol.