Allow Y Scales to independently fit data bounds of split charts

[jgough]

A long-standing feature request on Kibana since 2014 is to add functionality to allow independent y-scales on multiple charts displayed with the "Split chart" functionality.

At the time of writing the original Kibana issue has 70 thumbs-up reactions making it one of the most requested features in Kibana that has never been implemented.

For example, if I split a chart and one item is significantly more common than the other then I get this rather unhelpful graph:

It would be extremely useful to have a checkbox to scale the data bounds of each split chart independently, resulting in something like this mockup:

Bringing this feature request over to here since there seems to be high demand for this.

[ahopp]

@jgough Thanks for opening! I wonder if we can take an iterative approach and start with a manual setting at first then add automatic scaling.

[jgough]

Additionally, it would be very nice to add the ability to hide buckets with zero results from split charts

For example in this visualisation on playground there are many buckets shown in the split on the right that don't have any values. Having a checkbox to hide them would be wonderful.