[libp2p-dns] Implement /dnsaddr resolution. (#1931)

* Implement `/dnsaddr` support on `libp2p-dns`.

To that end, since resolving `/dnsaddr` addresses needs
"fully qualified" multiaddresses when dialing, i.e. those
that end with the `/p2p/...` protocol, we make sure that
dialing always uses such fully qualified addresses by
appending the `/p2p` protocol as necessary. As a side-effect,
this adds support for dialing peers via "fully qualified"
addresses, as an alternative to using a `PeerId` together
with a `Multiaddr` with or without the `/p2p` protocol.

* Adapt libp2p-relay.

* Update versions, changelogs and small cleanups.

misc/multistream-select/src/dialer_select.rs

@@ -260,7 +260,7 @@ where
                             let protocol = this.protocols.next().ok_or(NegotiationError::Failed)?;
                             *this.state = SeqState::SendProtocol { io, protocol }
                         }
-                        _ => return Poll::Ready(Err(ProtocolError::InvalidMessage.into())),
+                        _ => return Poll::Ready(Err(ProtocolError::InvalidMessage.into()))
                     }
                 }