Warn Cloud clusters about disk-full node adds (#22999)

* Warn Cloud clusters about disk-full node adds

Fixes DOC-15924

Summary of changes:

- Added a warning to avoid adding nodes when disks are nearly full and link to storage scaling guidance.

Author: rmloveland

src/current/cockroachcloud/advanced-cluster-management.md

@@ -41,6 +41,10 @@ These sections show how to scale a {{ site.data.products.advanced }} cluster hor
 
 You can add or remove nodes from your cluster through the Console. See [Planning your cluster]({% link cockroachcloud/plan-your-cluster.md %}) for cluster requirements and recommendations before proceeding.
 
+{{site.data.alerts.callout_danger}}
+Do not add nodes if your cluster's disks are nearly full. Adding nodes triggers rebalancing that can temporarily increase disk usage and worsen disk pressure. Instead, increase storage per node to create headroom. Refer to [Increase storage for a cluster](#increase-storage-for-a-cluster).
+{{site.data.alerts.end}}
+
 {{site.data.alerts.callout_info}}
 You cannot scale a multi-node cluster down to a single-node cluster.
 {{site.data.alerts.end}}