feat(quic): promote to stable release

- Cut a stable release of `libp2p-quic`.
- Export `libp2p-quic` as `libp2p::quic`.
- Update examples to use `libp2p-quic` through `libp2p`.

Pull-Request: #4325.

examples/relay-server/src/main.rs

@@ -31,11 +31,10 @@ use libp2p::{
     core::{Multiaddr, Transport},
     identify, identity,
     identity::PeerId,
-    noise, ping, relay,
+    noise, ping, quic, relay,
     swarm::{NetworkBehaviour, SwarmBuilder, SwarmEvent},
     tcp,
 };
-use libp2p_quic as quic;
 use std::error::Error;
 use std::net::{Ipv4Addr, Ipv6Addr};