swarm/: Enable advanced dialing requests (#2317)

Enable advanced dialing requests both on `Swarm` and via
`NetworkBehaviourAction`. Users can now trigger a dial with a specific
set of addresses, optionally extended via
`NetworkBehaviour::addresses_of_peer`. In addition the whole process is
now modelled in a type safe way via the builder pattern.

Example of a `NetworkBehaviour` requesting a dial to a specific peer
with a set of addresses additionally extended through
`NetworkBehaviour::addresses_of_peer`:

```rust
NetworkBehaviourAction::Dial {
    opts: DialOpts::peer_id(peer_id)
              .condition(PeerCondition::Always)
              .addresses(addresses)
              .extend_addresses_through_behaviour()
              .build(),
    handler,
}
```

Example of a user requesting a dial to an unknown peer with a single
address via `Swarm`:

```rust
swarm1.dial(
    DialOpts::unknown_peer_id()
        .address(addr2.clone())
        .build()
)
```

examples/ipfs-private.rs

@@ -265,7 +265,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     // Reach out to other nodes if specified
     for to_dial in std::env::args().skip(1) {
         let addr: Multiaddr = parse_legacy_multiaddr(&to_dial)?;
-        swarm.dial_addr(addr)?;
+        swarm.dial(addr)?;
         println!("Dialed {:?}", to_dial)
     }