add .debug bg to allow starting a battleground with just one player

it's implemented like .debug arena - so you toggle debug bg
on or off

src/game/debugcmds.cpp

@@ -521,6 +521,12 @@ bool ChatHandler::HandleGetItemState(const char* args)
     return true;
 }
 
+bool ChatHandler::HandleDebugBattlegroundCommand(const char * /*args*/)
+{
+    sBattleGroundMgr.ToggleTesting();
+    return true;
+}
+
 bool ChatHandler::HandleDebugArenaCommand(const char * /*args*/)
 {
     sBattleGroundMgr.ToggleArenaTesting();