[kbn/optimizer] only build xpack examples when building xpack plugins (#78656)

Co-authored-by: spalger <spalger@users.noreply.github.com>

x-pack/examples/alerting_example/public/components/documentation.tsx

@@ -0,0 +1,55 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+import React from 'react';
+
+import {
+  EuiText,
+  EuiPageBody,
+  EuiPageContent,
+  EuiPageContentBody,
+  EuiPageContentHeader,
+  EuiPageContentHeaderSection,
+  EuiPageHeader,
+  EuiPageHeaderSection,
+  EuiTitle,
+  EuiSpacer,
+} from '@elastic/eui';
+import { CreateAlert } from './create_alert';
+import { AlertingExampleComponentParams } from '../application';
+
+export const DocumentationPage = (deps: AlertingExampleComponentParams) => (
+  <EuiPageBody>
+    <EuiPageHeader>
+      <EuiPageHeaderSection>
+        <EuiTitle size="l">
+          <h1>Welcome to the Alerting plugin example</h1>
+        </EuiTitle>
+      </EuiPageHeaderSection>
+    </EuiPageHeader>
+    <EuiPageContent>
+      <EuiPageContentHeader>
+        <EuiPageContentHeaderSection>
+          <EuiTitle>
+            <h2>Documentation links</h2>
+          </EuiTitle>
+        </EuiPageContentHeaderSection>
+      </EuiPageContentHeader>
+      <EuiPageContentBody>
+        <EuiText>
+          <h2>Plugin Structure</h2>
+          <p>
+            This example solution has both `server` and a `public` plugins. The `server` handles
+            registration of example the AlertTypes, while the `public` handles creation of, and
+            navigation for, these alert types.
+          </p>
+        </EuiText>
+        <EuiSpacer />
+        <CreateAlert {...deps} />
+      </EuiPageContentBody>
+    </EuiPageContent>
+  </EuiPageBody>
+);