[charts][sankey] Make the default link color a lighter shade of the node color

[prakhargupta1]

Summary

Currently, the default link color in case of Automatic nodes is grey, and is being predominantly shown on the page.

In favor of making the page look more appealing, let's change the color of the links as lighter monochromatic shade of the node color, similar to what we have in case of Explicit nodes.

Examples

https://nivo.rocks/storybook/?path=/docs/sankey--docs
https://www.ag-grid.com/charts/react/sankey-series/

Search keywords: sankey

[github-actions]

This issue has been closed. If you have a similar problem but not exactly the same, please open a new issue.
Now, if you have additional information related to this issue or things that could help future readers, feel free to leave a comment.