Core/Creatures: Allow overriding default gossip menu id

Port From (https://github.com/TrinityCore/TrinityCore/commit/09568736134372ec1a79b936a248eec30f071c8d)

Source/Game/Entities/Creature/Creature.Fields.cs

@@ -28,6 +28,7 @@ namespace Game.Entities
 
         bool _isMissingCanSwimFlagOutOfCombat;
 
+        uint? _gossipMenuId;
         uint? _trainerId;
 
         public ulong m_PlayerDamageReq;

Source/Game/Entities/Creature/Creature.cs

@@ -1138,6 +1138,19 @@ namespace Game.Entities
         public bool HasFlag(CreatureStaticFlags7 flag)  { return _staticFlags.HasFlag(flag); }
         public bool HasFlag(CreatureStaticFlags8 flag)  { return _staticFlags.HasFlag(flag); }
 
+        public uint GetGossipMenuId()
+        {
+            if (_gossipMenuId.HasValue)
+                return _gossipMenuId.Value;
+
+            return GetCreatureTemplate().GossipMenuId;
+        }
+
+        public void SetGossipMenuId(uint? gossipMenuId)
+        {
+            _gossipMenuId = gossipMenuId;
+        }
+        
         public uint GetTrainerId()
         {
             if (_trainerId.HasValue)

Source/Game/Entities/Player/Player.cs

@@ -2698,7 +2698,7 @@ namespace Game.Entities
             switch (source.GetTypeId())
             {
                 case TypeId.Unit:
-                    return source.ToCreature().GetCreatureTemplate().GossipMenuId;
+                    return source.ToCreature().GetGossipMenuId();
                 case TypeId.GameObject:
                     return source.ToGameObject().GetGoInfo().GetGossipMenuId();
                 default:

Source/Game/Handlers/NPCHandler.cs

@@ -153,7 +153,7 @@ namespace Game
             _player.PlayerTalkClass.ClearMenus();
             if (!unit.GetAI().OnGossipHello(_player))
             {
-                GetPlayer().PrepareGossipMenu(unit, unit.GetCreatureTemplate().GossipMenuId, true);
+                GetPlayer().PrepareGossipMenu(unit, unit.GetGossipMenuId(), true);
                 GetPlayer().SendPreparedGossip(unit);
             }
         }

Source/Game/Handlers/QuestHandler.cs

@@ -68,7 +68,7 @@ namespace Game
             if (creature.GetAI().OnGossipHello(_player))
                 return;
 
-            GetPlayer().PrepareGossipMenu(creature, creature.GetCreatureTemplate().GossipMenuId, true);
+            GetPlayer().PrepareGossipMenu(creature, creature.GetGossipMenuId(), true);
             GetPlayer().SendPreparedGossip(creature);
         }