fix(spp_graduation): add web_icon to Graduation root menu

The openspp-graduation-menu-icons.png file existed in static/description
but was not referenced by the menu. Added web_icon attribute to display
the icon on the Graduation top-level menu.

Author: emjay0921

spp_graduation/views/graduation_menus.xml

@@ -5,6 +5,7 @@
         id="menu_graduation_root"
         name="Graduation"
         sequence="60"
+        web_icon="spp_graduation,static/description/openspp-graduation-menu-icons.png"
         groups="group_spp_graduation_user"
     />