[SIP-8] Add UI component for user to select and persist category color from Dashboard

[graceguo-supercat]

Make sure these boxes are checked before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if any
• I have reproduced the issue with at least the latest released version of superset
• I have checked the issue tracker for the same issue and I haven't found one similar

Superset version

0.27

Expected results

• User can use a color picker to choose specific color for chart category.
• With or without define color for chart, each time we refresh dashboard should see same category with a same color.

Actual results

Steps to reproduce

Refresh dashboard a few times.

Design

Implementation

• Reuse existed API to store category color in dashboard metadata
• refactory color assignment logic [Improve categorical color management #5815]
• Add color picker UI component (shown in design section) as part of dashboard builder control.

@williaster @elibrumbaugh @kristw @mistercrunch @michellethomas @john-bodley @betodealmeida @xtinec

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[junlincc]

closing the SIP as we added the project to roadmap apache-superset/superset-roadmap#110

cc @mihir174 this project requires design