Make public addresses go first in authority discovery DHT records (#3757)

Make sure explicitly set by the operator public addresses go first in
the authority discovery DHT records.

Also update `Discovery` behavior to eliminate duplicates in the returned
addresses.

This PR should improve situation with
https://github.com/paritytech/polkadot-sdk/issues/3519.

Obsoletes https://github.com/paritytech/polkadot-sdk/pull/3657.

substrate/client/authority-discovery/src/lib.rs

@@ -80,6 +80,10 @@ pub struct WorkerConfig {
 	/// Defaults to `true` to avoid the surprise factor.
 	pub publish_non_global_ips: bool,
 
+	/// Public addresses set by the node operator to always publish first in the authority
+	/// discovery DHT record.
+	pub public_addresses: Vec<Multiaddr>,
+
 	/// Reject authority discovery records that are not signed by their network identity (PeerId)
 	///
 	/// Defaults to `false` to provide compatibility with old versions
@@ -104,6 +108,7 @@ impl Default for WorkerConfig {
 			// `authority_discovery_dht_event_received`.
 			max_query_interval: Duration::from_secs(10 * 60),
 			publish_non_global_ips: true,
+			public_addresses: Vec::new(),
 			strict_record_validation: false,
 		}
 	}