Allow introducing own svgs for edges

[MeMeMax]

I would like to introduce my own svgs for edges. To be concrete I would like to have a dashed edge where each dash is a small arrow heading towards the target node (ignore the oval with the "+" - thats a label):

[lukasz-jazwa]

At the moment, custom SVG shapes for edges aren’t supported. You can style the existing edge path (https://www.ngdiagram.dev/docs/guides/edges/custom-edges/#available-css-variables), but replacing the edge rendering with your own SVG isn’t possible with the current API.

This is a limitation of the library rather than something that can be worked around externally. We’re aware this could be a useful capability, and we’ll need to evaluate how to support it properly and prioritize it with other improvements. I can’t commit to a timeline right now, but I’ll update here once we have more clarity.