Add support for clickable hover text or a per pt onclick attribute

Users can put links inside hover labels, but when user try to click the link, the hover label obviously disappears. So perhaps we could add optional “sticky” hover labels, where you click and the hover label is persistent until you click again?

Defining what sticky means will be tricky. It probably doesn't apply to every situation. Maybe we could add it as a new layout.hovermode e.g. 'hovermode: 'sticky'.

So, maybe instead we could define a linkonclick attribute e.g. linkonclick: ['https://plot.ly/~empet/101', 'https://plot.ly', /* ... one link per data pt */] that way clicking on a data pt would open the link instead of hovering on the data pt -> move mouse over link in hover label -> click on it.

cc @jackparmer

No se identifica ningún archivo, prueba ni punto de entrada. Primero hay que aclarar si el comportamiento previsto son etiquetas de hover persistentes o enlaces por punto al hacer clic; se considera terminado cuando la interacción está definida de forma inequívoca y la implementación coincide con ella.