SS port - Change extrusion role gcode (#2459)

implement custom gcode for when the extrusion role is changed

Co-authored-by: supermerill <merill@free.fr>

src/libslic3r/PrintConfig.hpp

@@ -969,6 +969,7 @@ PRINT_CONFIG_CLASS_DEFINE(
     ((ConfigOptionBool,                single_extruder_multi_material_priming))
     ((ConfigOptionBool,                wipe_tower_no_sparse_layers))
     ((ConfigOptionString,              change_filament_gcode))
+    ((ConfigOptionString,              change_extrusion_role_gcode))
     ((ConfigOptionFloat,               travel_speed))
     ((ConfigOptionFloat,               travel_speed_z))
     ((ConfigOptionBool,                silent_mode))