[APM] Add logic to setup default landing page for serverless (#158916)

Closes https://github.com/elastic/kibana/issues/158457
## Summary

This PR add default landing page for serverless based on comments
provided here -
https://github.com/elastic/kibana/issues/158457#issuecomment-1570760274

config/serverless.oblt.yml

@@ -12,7 +12,7 @@ xpack.serverless.observability.enabled: true
 xpack.infra.logs.app_target: discover
 
 ## Set the home route
-uiSettings.overrides.defaultRoute: /app/observabilityOnboarding
+uiSettings.overrides.defaultRoute: /app/observability/landing
 
 ## Set the dev project switch current type
 xpack.serverless.plugin.developer.projectSwitcher.currentType: 'observability'

x-pack/plugins/observability/public/pages/landing/landing.tsx

@@ -0,0 +1,32 @@
+/*
+ * 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 React from 'react';
+import { useHasData } from '../../hooks/use_has_data';
+import { useKibana } from '../../utils/kibana_react';
+
+export function LandingPage() {
+  const { hasDataMap, isAllRequestsComplete } = useHasData();
+  const {
+    application: { navigateToUrl },
+    http: { basePath },
+  } = useKibana().services;
+
+  if (isAllRequestsComplete) {
+    const { apm, infra_logs: logs } = hasDataMap;
+    const hasApmData = apm?.hasData;
+    const hasLogsData = logs?.hasData;
+
+    if (hasLogsData) {
+      navigateToUrl(basePath.prepend('/app/discover'));
+    } else if (hasApmData) {
+      navigateToUrl(basePath.prepend('/app/apm/services'));
+    } else {
+      navigateToUrl(basePath.prepend('/app/observabilityOnboarding'));
+    }
+  }
+  return <></>;
+}

x-pack/plugins/observability/public/routes/index.tsx

@@ -21,6 +21,7 @@ import { SlosWelcomePage } from '../pages/slos_welcome/slos_welcome';
 import { SloDetailsPage } from '../pages/slo_details/slo_details';
 import { SloEditPage } from '../pages/slo_edit/slo_edit';
 import { casesPath } from '../../common';
+import { LandingPage } from '../pages/landing/landing';
 
 export type RouteParams<T extends keyof typeof routes> = DecodeParams<typeof routes[T]['params']>;
 
@@ -60,7 +61,7 @@ export const routes = {
   },
   '/landing': {
     handler: () => {
-      return <SimpleRedirect to="/overview" />;
+      return <LandingPage />;
     },
     params: {},
     exact: true,