Update failover documentation with access note and failback

Added note about Azure Files access during failover and outlined planned failback process.

Author: guptasonia

articles/storage/common/storage-failover-customer-managed-planned.md

@@ -76,6 +76,8 @@ After the failover is complete, the original primary region becomes the new seco
 :::image type="content" source="media/storage-failover-customer-managed-common/post-failover-geo-redundant.png" alt-text="Diagram that shows the storage account status post-failover to secondary region." lightbox="media/storage-failover-customer-managed-common/post-failover-geo-redundant.png":::
 
 While in the failover state, perform your disaster recovery testing.
+> [!NOTE]
+> Azure Files access is stateful, so applications must remount file shares or restart after a planned or unplanned failover to establish new connections; otherwise, existing connections may fail.
 
 ### The planned failback process (GRS/RA-GRS)