Silky smooth discovery (#1274)

* Initial structural re-write

* Improving discovery update and correcting attestation service logic

* Rework discovery.mod

* Handling lifetimes of query futures

* Discovery update first draft

* format fixes

* Stabalise discv5 update

* Formatting corrections

* Limit FindPeers queries and bug correction

* Update to stable release discv5

* Remove unnecessary pin

* formatting

beacon_node/eth2_libp2p/src/metrics.rs

@@ -0,0 +1,28 @@
+pub use lighthouse_metrics::*;
+
+lazy_static! {
+    pub static ref ADDRESS_UPDATE_COUNT: Result<IntCounter> = try_create_int_counter(
+        "libp2p_address_update_total",
+        "Count of libp2p socked updated events (when our view of our IP address has changed)"
+    );
+    pub static ref PEERS_CONNECTED: Result<IntGauge> = try_create_int_gauge(
+        "libp2p_peer_connected_peers_total",
+        "Count of libp2p peers currently connected"
+    );
+    pub static ref PEER_CONNECT_EVENT_COUNT: Result<IntCounter> = try_create_int_counter(
+        "libp2p_peer_connect_event_total",
+        "Count of libp2p peer connect events (not the current number of connected peers)"
+    );
+    pub static ref PEER_DISCONNECT_EVENT_COUNT: Result<IntCounter> = try_create_int_counter(
+        "libp2p_peer_disconnect_event_total",
+        "Count of libp2p peer disconnect events"
+    );
+    pub static ref DISCOVERY_QUEUE: Result<IntGauge> = try_create_int_gauge(
+        "discovery_queue_size",
+        "The number of discovery queries awaiting execution"
+    );
+    pub static ref DISCOVERY_REQS: Result<IntGauge> = try_create_int_gauge(
+        "discovery_requests",
+        "The number of unsolicited discovery requests per second"
+    );
+}