[deck arcs] add JS hooks for sourceColor & targetColor

[mistercrunch]

Add a color picker for destination color and JS hooks for the mutator function to latch onto

@betodealmeida @hughhhh

[codecov-io]

Codecov Report

Merging #5706 into master will increase coverage by 0.41%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #5706      +/-   ##
==========================================
+ Coverage   63.45%   63.86%   +0.41%     
==========================================
  Files         361      361              
  Lines       22972    23501     +529     
  Branches     2557     2609      +52     
==========================================
+ Hits        14576    15010     +434     
- Misses       8381     8476      +95     
  Partials       15       15

Impacted Files	Coverage Δ
superset/assets/src/visualizations/word_cloud.js	0% <ø> (ø)	⬆️
superset/assets/src/explore/visTypes.jsx	62.16% <ø> (+5.01%)	⬆️
superset/assets/src/explore/controls.jsx	42.48% <ø> (-3.79%)	⬇️
...sualizations/deckgl/CategoricalDeckGLContainer.jsx	0% <0%> (ø)	⬆️
...et/assets/src/visualizations/deckgl/layers/arc.jsx	0% <0%> (ø)	⬆️
superset/viz.py	82.74% <0%> (+1.37%)	⬆️
superset/assets/src/visualizations/BigNumber.jsx	1.57% <0%> (+1.57%)	⬆️
superset/models/helpers.py	88.03% <0%> (+2.05%)	⬆️
superset/connectors/sqla/models.py	83% <0%> (+4.37%)	⬆️
... and 2 more

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[betodealmeida]

<3 it, it's beautiful!