SPIGOT-2776: Add Nitwit profession

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/Villager.java

@@ -138,6 +138,10 @@ public interface Villager extends Ageable, NPC, InventoryHolder {
          * Butcher profession. Wears a white apron.
          */
         BUTCHER(false),
+        /**
+         * Nitwit profession. Wears a green apron, cannot trade.
+         */
+        NITWIT(false),
         /**
          * Husk. <b>Reserved for Zombies</b>
          */