Cover replication_lag metric

Author: jonels-msft

articles/postgresql/hyperscale/concepts-monitoring.md

@@ -60,6 +60,7 @@ These metrics are available for Hyperscale (Citus) nodes:
 |memory_percent|Memory percent|Percent|The percentage of memory in use.|
 |network_bytes_ingress|Network In|Bytes|Network In across active connections.|
 |network_bytes_egress|Network Out|Bytes|Network Out across active connections.|
+|replication_lag|Replication Lag|Seconds|How far read replica nodes are behind their counterparts in the primary cluster.|
 |storage_percent|Storage percentage|Percent|The percentage of storage used out of the server's maximum.|
 |storage_used|Storage used|Bytes|The amount of storage in use. The storage used by the service may include the database files, transaction logs, and the server logs.|
 

articles/postgresql/hyperscale/concepts-read-replicas.md

@@ -101,12 +101,8 @@ There are two common scenarios for promoting a replica:
    the replica.  To avoid potentially losing data during promotion, you may want
    to disable writes to the original server group after the replica catches up.
 
-   > [!NOTE]
-   >
-   > There isn't yet a way in the Azure portal to view replication lag. To
-   > determine when a replica has sufficiently caught up, you can insert a signal
-   > row in a table of the original server group, and wait for it to appear in the
-   > replica.
+   You can see how far a replica has caught up with the `replication_lag` metric.
+   See [metrics](concepts-monitoring.md#metrics) for more information.
 
 ## Considerations