[Lens] Expose texture settings for bars and areas in Lens

[flash1293]

elastic/elastic-charts#1138 adds textures to elastic-charts

As this is a useful feature to improve a11y, it should be exposed in Lens as a setting.

I propose to not allow the user to edit every minor detail of the textures but only expose a simple switch.
If this switch is set, we will use the color of a series as a hash to select one of a limited number (maybe 20) "good" texture presets which will be used for the different series.

[elasticmachine]

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