Remove `visualization:colorMapping` Advanced Setting

The visualization:colorMapping setting was a tentative way to link colors to terms and reuse them across AggBased and TSVB charts.

This coloring mechanism takes place when one of the terms configured in the setting is also one of the terms passed to the chart. If that term defines a color association in the chart, then the color configured in the setting will take precedence over the default one.

This color mapping feature is only working with the compatibility palette, the default color palette used in Kibana 6.

The goal of this setting was to reuse the same colors across charts with the same terms in a dashboard, but due to its nature, an Advanced Settings applied to every chart in the same Space, it was difficult to master and use correctly. For example, you decided to associate to the term US the color red, but the term US can appear in different contexts and different dashboards where you are not interested in using the same color, but applying a different one or just the default. Applying these color mapping configurations should belong to the visualization or dashboard level, not at that higher level.

Lens never used this setting. We instead provide a per-chart color mapping feature (released as tech preview in 8.11 but going GA soon) with way more capabilities and configuration options than the mentioned setting.

Tasks:

[ ] Remove completely the settings and all the associated code
[ ] Provide a descriptive release note with the suggestion to use/switch to Lens and use the new color mapping.

elastic / kibana

Remove `visualization:colorMapping` Advanced Setting #193682