Alerting: Allow to clear datasource selection in panel list (#77960)

* Allow to clear datasource selection

Also improve texts for linked alerts switch

* Remove onClear prop as it does not work

* Change text on datasource selection filter

* Change datasource filter description

public/app/plugins/panel/alertlist/module.tsx

@@ -2,7 +2,7 @@ import React from 'react';
 
 import { DataSourceInstanceSettings, PanelPlugin } from '@grafana/data';
 import { config } from '@grafana/runtime';
-import { TagsInput } from '@grafana/ui';
+import { Button, Stack, TagsInput } from '@grafana/ui';
 import { OldFolderPicker } from 'app/core/components/Select/OldFolderPicker';
 import {
   ALL_FOLDER,
@@ -228,8 +228,8 @@ const unifiedAlertList = new PanelPlugin<UnifiedAlertListOptions>(UnifiedAlertLi
     })
     .addBooleanSwitch({
       path: 'dashboardAlerts',
-      name: 'Alerts from this dashboard',
-      description: 'Show alerts from this dashboard',
+      name: 'Alerts linked to this dashboard',
+      description: 'Only show alerts linked to this dashboard',
       defaultValue: false,
       category: ['Options'],
     })
@@ -250,19 +250,23 @@ const unifiedAlertList = new PanelPlugin<UnifiedAlertListOptions>(UnifiedAlertLi
     .addCustomEditor({
       path: 'datasource',
       name: 'Datasource',
-      description: 'Filter alerts from selected datasource',
+      description: 'Filter from alert source',
       id: 'datasource',
       defaultValue: null,
       editor: function RenderDatasourcePicker(props) {
         return (
+          <Stack gap={1}>
             <DataSourcePicker
               {...props}
               type={['prometheus', 'loki', 'grafana']}
               noDefault
               current={props.value}
               onChange={(ds: DataSourceInstanceSettings) => props.onChange(ds.name)}
-            onClear={() => props.onChange(null)}
             />
+            <Button variant="secondary" onClick={() => props.onChange(null)}>
+              Clear
+            </Button>
+          </Stack>
         );
       },
       category: ['Filter'],