[v10.4.x] Docs note on Cross-account observability permissions for CW datasource (#95123)

Co-authored-by: Jara Suárez de Puga García <jara.suarezdepuga@grafana.com>

docs/sources/datasources/aws-cloudwatch/_index.md

@@ -226,6 +226,10 @@ You can attach these permissions to the IAM role or IAM user you configured in [
 }
 ```
 
+{{< admonition type="note" >}}
+Cross-account observability lets you to retrieve metrics and logs across different accounts in a single region but you can't query EC2 Instance Attributes across accounts because those come from the EC2 API and not the CloudWatch API.
+{{< /admonition >}}
+
 ### Configure CloudWatch settings
 
 #### Namespaces of Custom Metrics