Update telemetry docs to include HA forwarding metrics. (#12611)

website/content/docs/internals/telemetry.mdx

@@ -217,6 +217,15 @@ These metrics relate to internal operations on Merkle Trees and Write Ahead Logs
 | `vault.wal.flushReady`                  | Time taken to flush a ready Write Ahead Log (WAL) to storage                | ms    | summary |
 | `vault.wal.flushReady.queue_len`        | Size of the write queue in the WAL system                                   | WAL   | summary |
 
+## HA Metrics
+
+These metrics are emitted on standbys when talking to the active node, and in some cases by performance standbys as well.
+
+| Metric                                  | Description                                                                 | Unit  | Type    |
+| :---------------------------------------| :---------------------------------------------------------------------------| :---- | :------ |
+| `vault.ha.rpc.client.forward`           | Time taken to forward a request from a standby to the active node           | ms    | summary |
+| `vault.ha.rpc.client.forward.errors`    | Number of standby request forwarding failures                               | errors| counter |
+
 ## Replication Metrics
 
 These metrics relate to [Vault Enterprise Replication](/docs/enterprise/replication). The following metrics are not available in telemetry unless replication is in an unhealthy state: `replication.fetchRemoteKeys`, `replication.merkleDiff`, and `replication.merkleSync`.