feature(sender): adapted relay and sender component to work with a simple transfer name

In order to be able to use a simple transfer name, the relay server and
the sender were adapted. On the sender, the on_create_room method was
adapted so that a call is made to the http_client to register the
transfer with the relay server. The handle_create_room method on the
server has been adapted so that when a room is created, the name is
transmitted by the receiver and is no longer generated on the
relayserver.This was also done in preparation for integrating a local
relayserver for the direct connection between sender and receiver.

src/shared.rs

@@ -31,7 +31,8 @@ pub enum JsonPacket {
         id: String,
     },
     /// Sent from the client to ask to create a new room.
-    Create,
+    Create { id: Option<String> },
+    // Create,
     /// Sent from the client to ask to leave the current room.
     Leave,
 }