[Question] How to make a Color of link gradient

### What problem does this feature solve?

Hi,
I have a graph with a lot of link ,
is it possible to make the link gradient base of the Source and target
Like the source of the link is the start of the gradient with color 1 and the target is the end with color 2

(Right now its a basic gradient not related to the source or target)

### What does the proposed API look like?

`lineStyle:{
color: gradient( {sourceColor}, {targetColor} )`