ability to extend lines for thresholds and axes

In plotly, sometimes the lines don't go far enough, and it would be helpful to extend them.

Case 1: Multiple axes are not joined together. The x-axis line should connect all axes, not just the first 2. In the example image, I have drawn a red line where I think the x-axis should continue.

Case 2. I sometimes want to draw a target line on a chart; in this case, below the line would be "bad", resulting in a red bar, while above the line, would be good. To implement these, I have used a dedicated series, with a constant value. However, a target line should really a special case of a "grid" line, rather than a special case of a "data series", and it ought to extend right the way to the (appropriate) axis. I've drawn this in yellow on the chart below. (Even better, a target should be defined by a single value, rather than an array of repeated values).

Thanks very much :-)

Comienza reproduciendo los dos casos de gráficos descritos en el issue: conectar un eje x entre varios ejes y extender una línea horizontal de objetivo o de cuadrícula hasta el eje correspondiente. Revisa los puntos de entrada de renderizado de Plotly.js para los ejes, las líneas de cuadrícula y las series para determinar si requieren comportamientos independientes. Se considera terminado cuando ambos casos funcionan sin representar un objetivo como una serie de datos repetida, con pruebas que cubran las extensiones resultantes de las líneas.