Describe hovering and z-order reordering in interactive docs

[joelostblom]

Include an example of how to bring points to top when hovered as here https://github.com/vega/vega-lite/pull/9136

[btwshivam]

I want to work on it. assign me!

[joelostblom]

Thank you @shivam200446 , just to clarify what I had in mind when opening this issue. I think we can add a short section to the interactive docs page (not the gallery) that explains how to create a hover ('mouseup'/'pointerup') interaction in a chart and then one more example that demonstrates the z-ordering as in the linked example below. I think that is a good base, but feel free to make suggestions of your own in the PR as well