Merge remote-tracking branch 'origin/unstable' into capella

Fixing the conflicts involved patching up some of the `block_hash` verification,
the rest will be done as part of https://github.com/sigp/lighthouse/issues/3870

beacon_node/client/src/builder.rs

@@ -174,6 +174,7 @@ where
             .monitor_validators(
                 config.validator_monitor_auto,
                 config.validator_monitor_pubkeys.clone(),
+                config.validator_monitor_individual_tracking_threshold,
                 runtime_context
                     .service_context("val_mon".to_string())
                     .log()

beacon_node/client/src/config.rs

@@ -1,3 +1,4 @@
+use beacon_chain::validator_monitor::DEFAULT_INDIVIDUAL_TRACKING_THRESHOLD;
 use directory::DEFAULT_ROOT_DIR;
 use environment::LoggerConfig;
 use network::NetworkConfig;
@@ -59,6 +60,11 @@ pub struct Config {
     pub validator_monitor_auto: bool,
     /// A list of validator pubkeys to monitor.
     pub validator_monitor_pubkeys: Vec<PublicKeyBytes>,
+    /// Once the number of monitored validators goes above this threshold, we
+    /// will stop tracking metrics on a per-validator basis. This prevents large
+    /// validator counts causing infeasibly high cardinailty for Prometheus and
+    /// high log volumes.
+    pub validator_monitor_individual_tracking_threshold: usize,
     #[serde(skip)]
     /// The `genesis` field is not serialized or deserialized by `serde` to ensure it is defined
     /// via the CLI at runtime, instead of from a configuration file saved to disk.
@@ -97,6 +103,7 @@ impl Default for Config {
             slasher: None,
             validator_monitor_auto: false,
             validator_monitor_pubkeys: vec![],
+            validator_monitor_individual_tracking_threshold: DEFAULT_INDIVIDUAL_TRACKING_THRESHOLD,
             logger_config: LoggerConfig::default(),
         }
     }