[Fleet] Mark shipper feature as experimental in Fleet UI (#154228)

Fixes https://github.com/elastic/kibana/issues/153845

## Summary

The new Outputs Shipper section will be available as an experimental
feature in 8.8.0. This PR adds a badge to clearly indicate it as
experimental in UI.



To test it:
Enable the shipper options by adding one of the following in outputs
yaml editor:

```
shipper: {}
```
OR
```
shipper:
  enabled: true
```

You should see a badge besides "Advanced options":
<img width="734" alt="Screenshot 2023-04-03 at 12 13 37"
src="https://user-images.githubusercontent.com/16084106/229481384-cce7d105-1e03-4e97-9815-a7cef3a29d11.png">
<img width="737" alt="Screenshot 2023-04-03 at 12 13 30"
src="https://user-images.githubusercontent.com/16084106/229481485-ff963b86-da9d-4f8e-ab23-277f7f9290f6.png">

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/fleet/public/applications/fleet/sections/settings/components/edit_output_flyout/advanced_options_section.tsx

@@ -19,6 +19,7 @@ import {
   EuiFieldText,
   EuiFieldNumber,
   EuiSelect,
+  EuiBetaBadge,
 } from '@elastic/eui';
 
 import { i18n } from '@kbn/i18n';
@@ -55,10 +56,17 @@ export const AdvancedOptionsSection: React.FunctionComponent<AdvancedOptionsSect
       id="advancedOutputOptions"
       arrowDisplay="left"
       buttonContent={
-        <FormattedMessage
-          id="xpack.fleet.settings.editOutputFlyout.advancedOptionsToggleLabel"
-          defaultMessage="Advanced options"
-        />
+        <EuiFlexGroup alignItems="flexStart">
+          <EuiFlexItem>
+            <FormattedMessage
+              id="xpack.fleet.settings.editOutputFlyout.advancedOptionsToggleLabel"
+              defaultMessage="Advanced options"
+            />
+          </EuiFlexItem>
+          <EuiFlexItem>
+            <EuiBetaBadge label="Experimental" color="subdued" />
+          </EuiFlexItem>
+        </EuiFlexGroup>
       }
     >
       <>