Additional networking metrics (#2549)

Adds additional metrics for network monitoring and evaluation.


Co-authored-by: Mark Mackey <mark@sigmaprime.io>

beacon_node/lighthouse_network/src/peer_manager/config.rs

@@ -16,6 +16,8 @@ pub struct Config {
     /* Peer count related configurations */
     /// Whether discovery is enabled.
     pub discovery_enabled: bool,
+    /// Whether metrics are enabled.
+    pub metrics_enabled: bool,
     /// Target number of peers to connect to.
     pub target_peer_count: usize,
 
@@ -34,6 +36,7 @@ impl Default for Config {
     fn default() -> Self {
         Config {
             discovery_enabled: true,
+            metrics_enabled: false,
             target_peer_count: DEFAULT_TARGET_PEERS,
             status_interval: DEFAULT_STATUS_INTERVAL,
             ping_interval_inbound: DEFAULT_PING_INTERVAL_INBOUND,