feat: allow deprioritizing servers for join requests

Implements #1549.

conduwuit-example.toml

@@ -1409,6 +1409,20 @@
 #
 #ignore_messages_from_server_names = []
 
+# List of server names that continuwuity will deprioritize (try last) when
+# a client requests to join a room.
+#
+# This can be used to potentially speed up room join requests, by
+# deprioritizing sending join requests through servers that are known to
+# be large or slow.
+#
+# continuwuity will still send join requests to servers in this list if
+# the room couldn't be joined via other servers it federates with.
+#
+# example: ["example.com"]
+#
+#deprioritize_joins_through_servers = []
+
 # Send messages from users that the user has ignored to the client.
 #
 # There is no way for clients to receive messages sent while a user was