Fix unaggregated delay metric (#8366)

while working on this #7892 @michaelsproul pointed it might be a good metric to measure the delay from start of the slot instead of the current `slot_duration / 3`, since the attestations duties start before the `1/3rd` mark now with the change in the link PR.


Co-Authored-By: hopinheimer <knmanas6@gmail.com>

Co-Authored-By: hopinheimer <48147533+hopinheimer@users.noreply.github.com>

beacon_node/beacon_chain/src/metrics.rs

@@ -1185,7 +1185,7 @@ pub static VALIDATOR_MONITOR_UNAGGREGATED_ATTESTATION_DELAY_SECONDS: LazyLock<
 > = LazyLock::new(|| {
     try_create_histogram_vec(
         "validator_monitor_unaggregated_attestation_delay_seconds",
-        "The delay between when the validator should send the attestation and when it was received.",
+        "The delay between when the validator sent the attestation and the start of the slot.",
         &["src", "validator"],
     )
 });

beacon_node/beacon_chain/src/validator_monitor.rs

@@ -1214,7 +1214,7 @@ impl<E: EthSpec> ValidatorMonitor<E> {
         let delay = get_message_delay_ms(
             seen_timestamp,
             data.slot,
-            slot_clock.unagg_attestation_production_delay(),
+            Duration::from_secs(0),
             slot_clock,
         );