Loki: Apply default_manage_alerts_ui_toggle config (#112297)

Datasources: Apply default_manage_alerts_ui_toggle config to Loki datasource

- Update AlertingSettings component to use config.defaultDatasourceManageAlertsUiToggle
- Change from options.jsonData.manageAlerts !== false to nullish coalescing operator
- Add comprehensive tests for config behavior
- Ensures consistency with Prometheus datasource implementation from PR #98441

Co-authored-by: Zoltán Bedi <zoltan.bedi@gmail.com>

public/app/plugins/datasource/loki/configuration/AlertingSettings.test.tsx

@@ -1,6 +1,8 @@
 import { render, screen } from '@testing-library/react';
 import userEvent from '@testing-library/user-event';
 
+import { config } from '@grafana/runtime';
+
 import { createDefaultConfigOptions } from '../mocks/datasource';
 
 import { AlertingSettings } from './AlertingSettings';
@@ -19,4 +21,43 @@ describe('AlertingSettings', () => {
     await userEvent.click(screen.getByRole('switch'));
     expect(onChange).toHaveBeenCalledTimes(1);
   });
+
+  describe('Switch checked behavior', () => {
+    describe('when options.jsonData.manageAlerts is unset', () => {
+      it('uses the config default `true`', () => {
+        const testOptions = createDefaultConfigOptions();
+        testOptions.jsonData.manageAlerts = undefined;
+
+        config.defaultDatasourceManageAlertsUiToggle = true;
+
+        render(<AlertingSettings options={testOptions} onOptionsChange={() => {}} />);
+
+        expect(screen.getByRole('switch')).toBeChecked();
+      });
+
+      it('uses the config default `false`', () => {
+        const testOptions = createDefaultConfigOptions();
+        testOptions.jsonData.manageAlerts = undefined;
+
+        config.defaultDatasourceManageAlertsUiToggle = false;
+
+        render(<AlertingSettings options={testOptions} onOptionsChange={() => {}} />);
+
+        expect(screen.getByRole('switch')).not.toBeChecked();
+      });
+    });
+
+    describe('when options.jsonData.manageAlerts is set', () => {
+      it.each([true, false])('uses the manageAlerts value even when the config default is %s', (configDefault) => {
+        const testOptions = createDefaultConfigOptions();
+        testOptions.jsonData.manageAlerts = true;
+
+        config.defaultDatasourceManageAlertsUiToggle = configDefault;
+
+        render(<AlertingSettings options={testOptions} onOptionsChange={() => {}} />);
+
+        expect(screen.getByRole('switch')).toBeChecked();
+      });
+    });
+  });
 });

public/app/plugins/datasource/loki/configuration/AlertingSettings.tsx

@@ -1,5 +1,6 @@
 import { DataSourcePluginOptionsEditorProps } from '@grafana/data';
 import { ConfigDescriptionLink, ConfigSubSection } from '@grafana/plugin-ui';
+import { config } from '@grafana/runtime';
 import { InlineField, InlineSwitch } from '@grafana/ui';
 
 export function AlertingSettings({
@@ -24,7 +25,7 @@ export function AlertingSettings({
         tooltip="Manage alert rules for this data source. To manage other alerting resources, add an Alertmanager data source."
       >
         <InlineSwitch
-          value={options.jsonData.manageAlerts !== false}
+          value={options.jsonData.manageAlerts ?? config.defaultDatasourceManageAlertsUiToggle}
           onChange={(event) =>
             onOptionsChange({
               ...options,