Add data retention and upgrade safety advice (#4440)

* add warning about data retention when uninstalling Control Center

* add TIP advice when upgrading Control Center

* use asciidoc format for admonitions

* apply PR suggestions

---------

Co-authored-by: Petter Holmström <petter@vaadin.com>

Author: sosa-vaadin

articles/control-center/getting-started/uninstall.adoc

@@ -18,6 +18,11 @@ helm uninstall installation-name -n installation-namespace
 
 Replace `installation-name` with the name of the Helm release you used when installing Control Center, and `installation-namespace` with the namespace where Control Center was installed.
 
+.Securing Your Data
+[WARNING]
+All Control Center-managed databases for all applications, including users, are deleted from the Kubernetes cluster when Control Center is uninstalled.
+If you want to retain the data, perform a <<../database/backups#,Backup>> before uninstalling.
+
 
 == Orphaned Applications
 

articles/control-center/getting-started/upgrade.adoc

@@ -26,6 +26,10 @@ helm upgrade --install control-center oci://docker.io/vaadin/control-center \
     --reuse-values
 ----
 
+.Securing Your Data
+[TIP]
+Although nothing should happen to Control Center-managed databases and users when upgrading, you should perform a <<../database/backups#,Backup>> before proceeding with an upgrade to prevent any data loss.
+
 
 == Upgrading from 1.0