go.Contour on top of px.xxxx_mapbox

@tvaucher You can plot only contour lines, by interpolating your data to get closed curves or just lines, in lon and lat coordinates, and then define mapbox_layers, as I did herehttps://community.plotly.com/t/circle-on-scattermapbox-with-coordinates-as-reference/36633/2 for such a closed curve.