Sandbox: e2e tests for apps running inside the frontend sandbox (#76357)

* Sandbox: Add tests for apps inside the sandbox

* Force type to prevent flawky test

e2e/custom-plugins/frontend-sandbox-app-test/module.js

@@ -0,0 +1,41 @@
+/*
+ * This is a dummy plugin to test the frontend sandbox
+ * It is not meant to be used in any other way
+ * This file doesn't require any compilation
+ */
+define(['react', '@grafana/data', 'react-router-dom'], function (React, grafanaData, ReactRouterDom) {
+  const { AppPlugin } = grafanaData;
+  const { Switch, Route } = ReactRouterDom;
+
+  function PageOne() {
+    return React.createElement(
+      'div',
+      {
+        'data-testid': 'sandbox-app-test-page-one',
+      },
+      'This is a page one'
+    );
+  }
+
+  function App() {
+    return React.createElement(Switch, null, React.createElement(Route, { component: PageOne }));
+  }
+  function AppConfig() {
+    return React.createElement(
+      'div',
+      {
+        'data-testid': 'sandbox-app-test-config-page',
+      },
+
+      'This is a config page'
+    );
+  }
+
+  const plugin = new AppPlugin().setRootPage(App).addConfigPage({
+    title: 'Configuration',
+    icon: 'cog',
+    body: AppConfig,
+    id: 'configuration',
+  });
+  return { plugin };
+});