fix(Core/BattlegroundAV): spawn generic gameobjects in Alterac Valley (#18764)

* fix(Scripts/PVP): correctly spawn generic gameobjects in Alterac Valley

I've been "collecting" these in the DB for a while, now it's time to move
these spawns to the AV script and actually spawn them.

* add 2 additional generic gameobjects

data/sql/updates/pending_db_world/rev_1713526355691722800.sql

@@ -0,0 +1,3 @@
+-- clear all gameobjects in map 30 "Alterac Valley"
+-- these will be spawned in the bg script
+DELETE FROM `gameobject` WHERE `map` = 30;