message: [consensus] add counter for sync_only visibility
  Closes:
diff: @@ -199,6 +199,9 @@ impl RoundManager {
  storage: Arc<dyn PersistentLivenessStorage>,
  sync_only: bool,
  ) -> Self {
  + counters::OP_COUNTERS
  + .gauge("sync_only")
  + .set(sync_only as i64);
  Self {
  epoch_state,
  block_store,
  