[Lens] Table dynamic coloring: compute overall gradient for split columns

[dej611]

Describe the feature:

The current implementation of dynamic coloring in Lens datatable computes the gradient min/max values per column in isolation.
This could lead to confusing results when using split columns/transposed columns feature as the same value may have assigned a different color.

@mbondyra reported some feedback here:

When having a split columns setup, the gradient is calculated for each column in separation which results to results like this one ('1' has the color of '0' as it's the smallest value for this column):

I agree with the opinion above and this it would be worth to let the user choose how the gradient should be computed in this case:

Transposable columns

How should range be computed for Transposable columns?
This is probably a general "range" discussion about Transposable columns, but in this context, it would be nice to make it clear.
At the moment each column computes its own range and colors are associated in "column isolation".
I may see that in some context it would be nice to have an "overall" range computed for the dimension transposed.
Is the current decision ok? Should I open a new issue for the "overall" option?

Also, maybe we should allow users to choose how to treat missing values as right now in this
chart we sometimes fill empty intervals with '0' and sometimes '-'. The logic we follow for count is to fill the empty intervals with 0 if they lay between truthy values, and '-' if not. So basically in both charts above '0' and '-' is the same thing.

[elasticmachine]

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

[flash1293]

Fixed by #95217