Add 404 error page (#4076)

* Add a 404 page

Signed-off-by: Fanit Kolchina <kolchfa@amazon.com>

* Add header

Signed-off-by: Fanit Kolchina <kolchfa@amazon.com>

* Reword

Signed-off-by: Fanit Kolchina <kolchfa@amazon.com>

* Reword sentence

Signed-off-by: Fanit Kolchina <kolchfa@amazon.com>

---------

Signed-off-by: Fanit Kolchina <kolchfa@amazon.com>

404.md

@@ -1,17 +1,11 @@
 ---
 permalink: /404.html
-layout: error
-errormessage: 🙅‍♀️ 404
-body_class: homepage
-errorhuman: "OpenSearch can't find that page." 
+title: 404
+layout: default
+heading_anchors: false
+nav_exclude: true
 ---
 
-Sorry about that. Perhaps we moved something around, or you mistyped the URL? 
-
-
-Head to the [OpenSearch Documentation home page](https://opensearch.org/docs/latest/) or try our [community forum](https://forum.opensearch.org/).
-
-
-
-
+# OpenSearch cannot find that page. 
 
+Perhaps we moved something around, or you mistyped the URL? Try using search or go to the [OpenSearch Documentation home page](https://opensearch.org/docs/latest/). If you need further help, see the [OpenSearch community forum](https://forum.opensearch.org/).

_layouts/default.html

@@ -52,7 +52,7 @@ layout: table_wrappers
     <div id="main-header"></div>
     <div class="side-bar">
       <div class="site-header">
-        <a href="#" id="menu-button" class="site-button">
+        <a href="/docs/latest/" id="menu-button" class="site-button">
           Documentation <svg viewBox="0 0 24 24" class="icon"><use xlink:href="#svg-grid"></use></svg>
         </a>
       </div>
@@ -102,7 +102,7 @@ layout: table_wrappers
     </div>
     <div class="copy-banner">
       <div class="container">
-        <h1><a href="#">Documentation</a></h1>
+        <h1><a href="/docs/latest/">Documentation</a></h1>
         {% if site.search_enabled != false or site.use_custom_search == true %}
         <div class="search">
           <div class="search-input-wrap">