Edges/Ports should support children property (similar to Nodes)

[Vadorequest]

Currently, the Edge component doesn't support the children property. (or, actually, it does, but does nothing with it)

I think the Edge children should behave similarly to the Nodes, and accept either a component or a function that returns a react component.

I can make a PR for this.

[amcdnl]

Whats the use case for this? Doesn't make sense to me.

[Vadorequest]

Allowing the use of foreignObject as children, and draw custom HTML elements such as additional buttons of a different style to replace the built-in Add/Remove components (and other options)

I intend to use it to build my own Add/Remove buttons on edges, with actual HTML/CSS instead of SVG.

[Vadorequest]

The same logic applies to ports as well.

I need to display an icon/text next to each port.
For instance, it would be a warning when a port isn't connected with any other node.

I think the same PR should bring support for children in both Ports and Edges.