Core/SmartAI: add param2 to SMART_ACTION_UPDATE_TEMPLATE, allowing to specify if creature's level should remain the same between entry updates.

A value of 0 (default) forces the creature to keep its current level between entry updates.

Fixes #16371

src/server/game/AI/SmartScripts/SmartScript.cpp

@@ -1013,7 +1013,7 @@ void SmartScript::ProcessAction(SmartScriptHolder& e, Unit* unit, uint32 var0, u
 
             for (ObjectList::const_iterator itr = targets->begin(); itr != targets->end(); ++itr)
                 if (IsCreature(*itr))
-                    (*itr)->ToCreature()->UpdateEntry(e.action.updateTemplate.creature);
+                    (*itr)->ToCreature()->UpdateEntry(e.action.updateTemplate.creature, nullptr, e.action.updateTemplate.updateLevel);
 
             delete targets;
             break;