Implement status v2 version (#7590)

N/A


  Implements status v2 as defined in https://github.com/ethereum/consensus-specs/pull/4374/

beacon_node/network/src/sync/backfill_sync/mod.rs

@@ -1243,6 +1243,7 @@ mod tests {
                         head_root: Hash256::random(),
                         finalized_epoch,
                         finalized_root: Hash256::random(),
+                        earliest_available_slot: None,
                     },
                 },
             );