[SPARK-51104][DOC] Self-host JavaScript and CSS in Spark website

LICENSE

@@ -247,6 +247,7 @@ core/src/main/resources/org/apache/spark/ui/static/sorttable.js
 docs/js/vendor/anchor.min.js
 docs/js/vendor/jquery*
 docs/js/vendor/modernizer*
+docs/js/vendor/docsearch.min.js
 
 ISC License
 -----------

docs/_layouts/global.html

@@ -22,8 +22,7 @@
         {% endif %}
 
 
-        <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet"
-        integrity="sha384-EVSTQN3/azprG1Anm3QDgpJLIm9Nao0Yz1ztcQTwFspd3yD65VohhpuuCOmLASjC" crossorigin="anonymous">
+        <link rel="stylesheet" href="{{ rel_path_to_root }}css/bootstrap.min.css">
         <link rel="preconnect" href="https://fonts.googleapis.com">
         <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
         <link href="https://fonts.googleapis.com/css2?family=DM+Sans:ital,wght@0,400;0,500;0,700;1,400;1,500;1,700&Courier+Prime:wght@400;700&display=swap" rel="stylesheet">
@@ -193,15 +192,13 @@ <h1 class="title">{{ page.title }}</h1>
              <!-- /container -->
         </div>
 
-        <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js"
-        integrity="sha384-MrcW6ZMFYlzcLA8Nl+NtUVF0sA7MsXsP1UyJoMp4YLEuNSfAP+JcXn/tWtIaxVXM"
-        crossorigin="anonymous"></script>
-        <script src="https://code.jquery.com/jquery.js"></script>
+        <script src="{{ rel_path_to_root }}js/vendor/jquery-3.5.1.min.js"></script>
+        <script src="{{ rel_path_to_root }}js/vendor/bootstrap.bundle.min.js"></script>
 
         <script src="{{ rel_path_to_root }}js/vendor/anchor.min.js"></script>
         <script src="{{ rel_path_to_root}}js/main.js"></script>
 
-        <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/docsearch.js@2/dist/cdn/docsearch.min.js"></script>
+        <script type="text/javascript" src="{{ rel_path_to_root }}js/vendor/docsearch.min.js"></script>
         <script type="text/javascript">
             // DocSearch is entirely free and automated. DocSearch is built in two parts:
             // 1. a crawler which we run on our own infrastructure every 24 hours. It follows every link
@@ -241,6 +238,5 @@ <h1 class="title">{{ page.title }}</h1>
                     '?config=TeX-AMS-MML_HTMLorMML';
                 d.getElementsByTagName('head')[0].appendChild(script);
             }(document));
-        </script>
     </body>
 </html>