dataviz: move legend to bottom in narrow graphs (#39920)

combo/apps/dataviz/models.py

@@ -270,6 +270,8 @@ class ChartNgCell(CellBase):
                 else:
                     values = [data[i][j] for j in range(len(x_labels))]
                 chart.add(serie_label, values)
+            if width and width < 500:
+                chart.legend_at_bottom = True
         else:
             # pie, create a serie by data, to get different colours
             values = data