Validator monitor support for sync committees (#2476)

## Issue Addressed

N/A

## Proposed Changes

Add functionality in the validator monitor to provide sync committee related metrics for monitored validators.


Co-authored-by: Michael Sproul <michael@sigmaprime.io>

common/slot_clock/src/lib.rs

@@ -82,9 +82,21 @@ pub trait SlotClock: Send + Sync + Sized + Clone {
         self.slot_duration() / 3
     }
 
+    /// Returns the delay between the start of the slot and when sync committee messages should be
+    /// produced.
+    fn sync_committee_message_production_delay(&self) -> Duration {
+        self.slot_duration() / 3
+    }
+
     /// Returns the delay between the start of the slot and when aggregated attestations should be
     /// produced.
     fn agg_attestation_production_delay(&self) -> Duration {
         self.slot_duration() * 2 / 3
     }
+
+    /// Returns the delay between the start of the slot and when partially aggregated `SyncCommitteeContribution` should be
+    /// produced.
+    fn sync_committee_contribution_production_delay(&self) -> Duration {
+        self.slot_duration() * 2 / 3
+    }
 }