fix: process color scheme configs correctly

[suddjian]

SUMMARY

Loading custom sequential color schemes was failing because config objects were being treated as if they were instantiated classes.

TESTING INSTRUCTIONS

Add a custom sequential color scheme, and use it from a chart (sunburst chart uses sequential if you have both a primary and secondary metric)

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #17786 (633df3d) into master (d9acb28) will decrease coverage by 0.00%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##           master   #17786      +/-   ##
==========================================
- Coverage   67.72%   67.72%   -0.01%     
==========================================
  Files        1605     1605              
  Lines       64207    64211       +4     
  Branches     6790     6790              
==========================================
+ Hits        43482    43484       +2     
- Misses      18869    18871       +2     
  Partials     1856     1856              

Flag	Coverage Δ
javascript	54.82% <71.42%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ntend/packages/superset-ui-core/src/color/index.ts	100.00% <ø> (ø)
superset-frontend/src/setup/setupColors.ts	78.57% <71.42%> (-11.43%)	⬇️

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[ryankubin]

@suddjian Looks as good as the day I watched you do it, sorry for the late review!

[rosemarie-chiu]

🏷 2022.1