Add zorder argument for go.Scattermap

[ShootingStarD]

Would it be possible to add the argument zorder for the Scattermap? Just like for go.Bar and others?

In #4746 it was asked to make a feature request so here it is

[gvwilson]

Thanks @ShootingStarD - I've added it to our backlog and we'll see what we can do in the next work cycle.