feat(request-response): add modules for json and cbor messages

This patch adds two modules to `libp2p::request_response`:

- `cbor`
- `json`

Both define a `Behaviour` type-alias that comes with a `Codec` implementation which uses the respective `serde` crate to serialize and deserialize the messages.

Fixes libp2p#3905.

Pull-Request: libp2p#3952.

src/behaviour.rs

@@ -222,7 +222,7 @@ impl Behaviour {
         let protocols = iter::once((DEFAULT_PROTOCOL_NAME, ProtocolSupport::Full));
         let mut cfg = request_response::Config::default();
         cfg.set_request_timeout(config.timeout);
-        let inner = request_response::Behaviour::new(AutoNatCodec, protocols, cfg);
+        let inner = request_response::Behaviour::with_codec(AutoNatCodec, protocols, cfg);
         Self {
             local_peer_id,
             inner,