docs(acpt): add retention step (#4785)

Author: nerda-codes

pages/cockpit/how-to/create-external-data-sources.mdx

@@ -28,12 +28,11 @@ This page shows you how to create a **custom** [data source](/cockpit/concepts/#
     <Message type="tip">
       We recommend that you create your data sources in the same regions as the alert manager if you want to receive alerts for them.
     </Message>
-7. Leave the default [retention period](/cockpit/concepts/#retention) or adjust it as you wish.
-    <Message type="note">
-      Extending the retention period above the default one could incur addtional costs.
-    </Message>
-8. Click **Create custom data source**.
-
-<Message type="note">
-  If you are using Scaleway resources integrated with Cockpit, you can also view your Scaleway data sources in the **Data sources** tab. Scaleway data sources are **read-only**.
-</Message>
+7. Drag the slider to adjust the [retention period](/cockpit/concepts/#retention) for your data source:
+    - Drag the slider to the **right to increase** your retention period, or
+    - Drag the slider to the **left to decrease** the retention period.
+        <Message type="important">
+         - Reducing the retention period of a data source will permanently delete all observability data in that data source beyond the selected timeframe. This deletion is irreversible and takes effect a few minutes after the retention period is reduced, even if the retention period is later increased.
+         - Find out about the [retention periods available for each data source type](/cockpit/concepts/#retention).
+        </Message>
+8. Click **Create custom data source**.