docs(alerting): clarify behaviour when provisioning the policy tree (#101937)

docs/sources/shared/alerts/alerting_provisioning.md

@@ -1386,6 +1386,8 @@ Status: Conflict
 
 ### <span id="route-put-policy-tree"></span> Sets the notification policy tree. (_RoutePutPolicyTree_)
 
+{{< docs/shared lookup="alerts/warning-provisioning-tree.md" source="grafana" version="<GRAFANA_VERSION>" >}}
+
 ```
 PUT /api/v1/provisioning/policies
 ```

docs/sources/shared/alerts/warning-provisioning-tree.md

@@ -0,0 +1,9 @@
+---
+title: 'Warning Provisioning Tree'
+---
+
+{{% admonition type="warning" %}}
+
+Since the policy tree is a single resource, provisioning it will overwrite all policies in the notification policy tree. However, it does not affect internal policies created when alert rules directly select a contact point.
+
+{{< /admonition >}}