Reverse zorder in ensemble plot

In commit c580f1d
reversed chronologically sorting of ensembles was added
in the  EnsembleSelectionWidget. This affected the drawing order of
iterations, making the newer iterations hide the older iterations when
using the default sorting order. This commit remedies this by reversing
the zorder of plots, so that the first ensembles in the selection list will
be drawn on top of the later ensembles.

(cherry picked from commit 5305871)

Author: HakonSohoel

src/ert/gui/tools/plot/plottery/plots/ensemble.py

@@ -38,7 +38,7 @@ def plot(
         plot_context.y_axis = plot_context.VALUE_AXIS
         plot_context.x_axis = plot_context.DATE_AXIS
         draw_style = "steps-pre" if is_rate(plot_context.key()) else None
-
+        zorder = 0
         for ensemble, data in ensemble_to_data_map.items():
             data = data.T
 
@@ -53,7 +53,9 @@ def plot(
                     data,
                     f"{ensemble.experiment_name} : {ensemble.name}",
                     draw_style,
+                    zorder=zorder,
                 )
+                zorder -= 1
                 config.nextColor()
 
         plotObservations(observation_data, plot_context, axes)
@@ -75,6 +77,7 @@ def _plotLines(
         data: pd.DataFrame,
         ensemble_label: str,
         draw_style: str | None = None,
+        zorder: float = 1,
     ) -> None:
         style = plot_config.defaultStyle()
 
@@ -91,6 +94,7 @@ def _plotLines(
             linestyle=style.line_style,
             markersize=style.size,
             drawstyle=draw_style,
+            zorder=zorder,
         )
 
         if len(lines) > 0: