[ObsUX] Enable Hosts advanced setting on serverless (#170035)

Closes #169198

## Summary

* Adds Hosts advanced setting to the observability settings allowlist
* Adds tests for Hosts sidenav item visibility


https://github.com/elastic/kibana/assets/793851/3c9252c8-a4cb-4da8-aa60-23a8aeb60d4c

# How to test

* Run locally in serverless mode
* Make sure "Observability Hosts view" toggle is visible on the Advanced
Settings screen
* Toggle the setting on and off, make sure sidenav properly reacts to
the changes
* Go to Infra settings screen
* Toggle the same setting on and off, and also make sure sidenav
properly reacts to the changes

packages/serverless/settings/observability_project/index.ts

@@ -27,4 +27,5 @@ export const OBSERVABILITY_PROJECT_SETTINGS = [
   settings.OBSERVABILITY_APM_TRACE_EXPLORER_TAB_ID,
   settings.OBSERVABILITY_ENABLE_AWS_LAMBDA_METRICS_ID,
   settings.OBSERVABILITY_APM_ENABLE_CRITICAL_PATH_ID,
+  settings.OBSERVABILITY_ENABLE_INFRASTRUCTURE_HOSTS_VIEW_ID,
 ];

x-pack/test_serverless/functional/page_objects/svl_common_navigation.ts

@@ -65,6 +65,17 @@ export function SvlCommonNavigationProvider(ctx: FtrProviderContext) {
           expect(await getByVisibleText('~nav-item', by.text)).not.be(null);
         }
       },
+      async expectLinkMissing(
+        by: { deepLinkId: AppDeepLinkId } | { navId: string } | { text: string }
+      ) {
+        if ('deepLinkId' in by) {
+          await testSubjects.missingOrFail(`~nav-item-deepLinkId-${by.deepLinkId}`);
+        } else if ('navId' in by) {
+          await testSubjects.missingOrFail(`~nav-item-id-${by.navId}`);
+        } else {
+          expect(await getByVisibleText('~nav-item', by.text)).be(null);
+        }
+      },
       async expectLinkActive(
         by: { deepLinkId: AppDeepLinkId } | { navId: string } | { text: string }
       ) {

x-pack/test_serverless/functional/test_suites/observability/infra/index.ts

@@ -10,6 +10,7 @@ import { FtrProviderContext } from '../../../ftr_provider_context';
 export default function ({ loadTestFile }: FtrProviderContext) {
   describe('Observability Infra', function () {
     loadTestFile(require.resolve('./header_menu'));
+    loadTestFile(require.resolve('./navigation'));
     loadTestFile(require.resolve('./node_details'));
     loadTestFile(require.resolve('./hosts_page'));
     loadTestFile(require.resolve('./infra'));

x-pack/test_serverless/functional/test_suites/observability/infra/navigation.ts

@@ -0,0 +1,63 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { enableInfrastructureHostsView } from '@kbn/observability-plugin/common';
+import { FtrProviderContext } from '../../../ftr_provider_context';
+
+export default ({ getPageObjects, getService }: FtrProviderContext) => {
+  const kibanaServer = getService('kibanaServer');
+  const svlObltNavigation = getService('svlObltNavigation');
+  const browser = getService('browser');
+  const pageObjects = getPageObjects(['svlCommonPage', 'svlCommonNavigation', 'header']);
+
+  const setHostsSetting = async (value: boolean) => {
+    await kibanaServer.uiSettings.update({ [enableInfrastructureHostsView]: value });
+    await browser.refresh();
+    await pageObjects.svlCommonNavigation.expectExists();
+  };
+
+  const openInfraSection = async () => {
+    await pageObjects.svlCommonNavigation.sidenav.openSection('observability_project_nav.metrics');
+  };
+
+  describe('Infra Side Navigation', () => {
+    before(async () => {
+      await pageObjects.svlCommonPage.login();
+      await svlObltNavigation.navigateToLandingPage();
+    });
+
+    after(async () => {
+      await pageObjects.svlCommonPage.forceLogout();
+    });
+
+    describe('when Hosts settings is on', () => {
+      before(async () => {
+        await setHostsSetting(true);
+        await openInfraSection();
+      });
+
+      it("shows the 'Hosts' nav item", async () => {
+        await pageObjects.svlCommonNavigation.sidenav.expectLinkExists({
+          deepLinkId: 'metrics:hosts',
+        });
+      });
+    });
+
+    describe('when Hosts settings is off', () => {
+      before(async () => {
+        await setHostsSetting(false);
+        await openInfraSection();
+      });
+
+      it("hides the 'Hosts' nav item", async () => {
+        await pageObjects.svlCommonNavigation.sidenav.expectLinkMissing({
+          deepLinkId: 'metrics:hosts',
+        });
+      });
+    });
+  });
+};