feat(discovery): add choropleth stepped continuous color mode

[davidlougheed]

WIP

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.76%. Comparing base (709033e) to head (bd59e97).

Files with missing lines	Patch %	Lines
bento_lib/discovery/models/overview.py	62.50%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #366      +/-   ##
===========================================
- Coverage   100.00%   99.76%   -0.24%     
===========================================
  Files           82       82              
  Lines         2515     2528      +13     
  Branches       231      233       +2     
===========================================
+ Hits          2515     2522       +7     
- Misses           0        6       +6     

Files with missing lines	Coverage Δ
bento_lib/discovery/models/overview.py	87.75% <62.50%> (-12.25%)	⬇️

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