feat(Core/Config): add option for LFG expansion (#7256)

src/server/worldserver/worldserver.conf.dist

@@ -1252,6 +1252,16 @@ DeletedCharacterTicketTrace = 0
 
 DungeonFinder.OptionsMask = 1
 
+#
+#     DungeonFinder.Expansion
+#        Description: Allow setting which expansion can be used in LFG
+#           2 - Wotlk (Default)
+#           1 - TBC
+#           0 - Classic
+#        Default:     2
+
+DungeonFinder.Expansion = 2
+
 #
 #   AccountInstancesPerHour
 #        Description: Controls the max amount of different instances player can enter within hour