[9371] Implement .reload all_gossips

* For reload `gossip_menu`, `gossip_menu_option`, `gossip_scripts`,
  `npc_gossip`, `points_of_interest` by single command.
* Also fixed reloading `points_of_interest`.

src/game/ObjectMgr.cpp

@@ -6424,6 +6424,8 @@ void ObjectMgr::LoadReputationOnKill()
 
 void ObjectMgr::LoadPointsOfInterest()
 {
+    mPointsOfInterest.clear();                              // need for reload case
+
     uint32 count = 0;
 
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