feat(Core/Config): Add parameter to load all grids of all non-instanced maps on server start (#2283)

src/server/game/Maps/Map.h

@@ -319,6 +319,7 @@ class Map : public GridRefManager<NGridType>
         }
 
         void LoadGrid(float x, float y);
+        void LoadAllCells();
         bool UnloadGrid(NGridType& ngrid);
         virtual void UnloadAll();