Add more Sankey examples

[techniq]

Add more Sankey examples

• [ ] Expandable (similar to Tree)
  • https://unovis.dev/gallery/view/?collection=Networks%20and%20Flows&title=Expandable%20Sankey
• [ ] Highlight downstream
  • https://observablehq.com/@bda/lafe
• [ ] d3-array rollup usage (with common downstream nodes)
• [ ] HTML labels
• [ ] Animated links
  • [ ] Animated gradients
  • [ ] Animated SVG gradient
• [ ] Flowing particles along a path
  • Particle Sankey