feature/add-supervisor-role-title

[evamaxfield]

Link to Relevant Issue

This pull request resolves https://github.com/CouncilDataProject/king-county/runs/5874063516?check_suite_focus=true

Description of Changes

Include a description of the proposed changes.

New Role found by King County scraper: "Supervisor"
This seems like an official enough role and doesn't overlap with any of the current roles so makes sense to add and allow it through the pipeline.

[codecov]

Codecov Report

Merging #180 (dea4ad6) into main (2e472b9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #180   +/-   ##
=======================================
  Coverage   94.67%   94.67%           
=======================================
  Files          50       50           
  Lines        2610     2611    +1     
=======================================
+ Hits         2471     2472    +1     
  Misses        139      139           

Impacted Files	Coverage Δ
cdp_backend/database/constants.py	100.00% <100.00%> (ø)

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