[8.9] [DOCS] Fix welcome-to-elastic link (#166357) (#166534)

# Backport

This will backport the following commits from `main` to `8.9`:
- [[DOCS] Fix `welcome-to-elastic` link
(#166357)](#166357)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"James
Rodewig","email":"[email protected]"},"sourceCommit":{"committedDate":"2023-09-14T10:08:35Z","message":"[DOCS]
Fix `welcome-to-elastic` link (#166357)\n\n**Problem:** In
elastic/docs#2752, we updated the URL prefix
(`welcome-to-elastic`) and name for the \"Welcome to Elastic Docs\"
docs. However, we still have some stray links that use the old
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Fix `welcome-to-elastic` link (#166357)\n\n**Problem:** In
elastic/docs#2752, we updated the URL prefix
(`welcome-to-elastic`) and name for the \"Welcome to Elastic Docs\"
docs. However, we still have some stray links that use the old
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Fix `welcome-to-elastic` link (#166357)\n\n**Problem:** In
elastic/docs#2752, we updated the URL prefix
(`welcome-to-elastic`) and name for the \"Welcome to Elastic Docs\"
docs. However, we still have some stray links that use the old
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BACKPORT-->

docs/landing-page.asciidoc

@@ -259,7 +259,7 @@
     </a>
   </div>
   <div class="col-md-4 col-12 mb-2">
-    <a class="no-text-decoration" href="https://www.elastic.co/guide/en/welcome-to-elastic/current/getting-started-observability.html">
+    <a class="no-text-decoration" href="https://www.elastic.co/guide/en/starting-with-the-elasticsearch-platform-and-its-solutions/current/getting-started-observability.html">
       <div class="card h-100">
         <h4 class="mt-3">
           <span class="inline-block float-left icon mr-2" style="background-image: url('https://images.contentstack.io/v3/assets/bltefdd0b53724fa2ce/bltaa08b370a00bbecc/634d9da14e565f1cdce27f7c/observability-logo-color-32px.png');"></span>