Support SOCKS5 protocol for replication

Using "socks5" as the protocol in the "proxy" parameter of replication
requests will cause DNS resolution and data transfer to happen via a
SOCKS5 proxy server.

COUCHDB-2025
diff --git a/src/couch_replicator_utils.erl b/src/couch_replicator_utils.erl
index 240d7d4..99ddebf 100644
--- a/src/couch_replicator_utils.erl
+++ b/src/couch_replicator_utils.erl
@@ -300,9 +300,10 @@
         host = Host,
         port = Port,
         username = User,
-        password = Passwd
+        password = Passwd,
+        protocol = Protocol
     } = ibrowse_lib:parse_url(ProxyUrl),
-    [{proxy_host, Host}, {proxy_port, Port}] ++
+    [{proxy_protocol, Protocol}, {proxy_host, Host}, {proxy_port, Port}] ++
         case is_list(User) andalso is_list(Passwd) of
         false ->
             [];