[Lens] Separate color dimension for all chart types

[flash1293]

It's already possible (resp. will be possible soon) to color pie slices, xy chart series and table cells by their current value or series name.

However in some cases, the coloring should happen by some other condition. It should be possible to specify a separate dimension/metric to do the coloring by.

An example use case is a bar chart of countries with some metric. The bar color should indicate the continent of the country. This would be possible by specifying a separate coloring dimension which is set to "last value" of the continent field.

Another example is a bar chart of revenues per product. The color should indicate whether the profit is positive or negative. In this case the separate coloring dimension would be set to a formula like sum(total) - sum(cost), in combination with a custom color palettes which with two colors (larger and smaller than 0)

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[ghudgins]

+1

we may want to look at displaying one thing but colouring by a different value, e.g. display hostname but colour on max cpu