Alerting: Add info to enable alert forwarding when using an external alertmanager (#69150)

public/app/plugins/datasource/alertmanager/ConfigEditor.tsx

@@ -1,9 +1,11 @@
 import produce from 'immer';
 import React from 'react';
+import { Link } from 'react-router-dom';
 
 import { SIGV4ConnectionConfig } from '@grafana/aws-sdk';
 import { DataSourcePluginOptionsEditorProps, SelectableValue } from '@grafana/data';
 import { DataSourceHttpSettings, InlineField, InlineFormLabel, InlineSwitch, Select } from '@grafana/ui';
+import { Span } from '@grafana/ui/src/unstable';
 import { config } from 'app/core/config';
 
 import { AlertManagerDataSourceJsonData, AlertManagerImplementation } from './types';
@@ -73,6 +75,11 @@ export const ConfigEditor = (props: Props) => {
             />
           </InlineField>
         </div>
+        {options.jsonData.handleGrafanaManagedAlerts && (
+          <Span variant="bodySmall" color="secondary">
+            Make sure to enable the alert forwarding on the <Link to="/alerting/admin">admin page</Link>.
+          </Span>
+        )}
       </div>
       <DataSourceHttpSettings
         defaultUrl={''}