Add matomo tracker for javadoc (#15326)

Author: pabloem

build-tools/build-infra/src/main/groovy/lucene.documentation.render-javadoc.gradle

@@ -389,10 +389,34 @@ abstract class RenderJavadocTask extends RenderJavadocTaskBase {
     }
 
     LuceneBuildGlobalsExtension buildGlobals = project.rootProject.extensions.getByType(LuceneBuildGlobalsExtension)
-    opts << [
-      '-bottom',
-      "<i>Copyright &copy; 2000-${buildGlobals.buildYear} Apache Software Foundation. All Rights Reserved.</i>"
-    ]
+    def copyright = "<i>Copyright &copy; 2000-${buildGlobals.buildYear} Apache Software Foundation. All Rights Reserved.</i>"
+    if (luceneDocUrl.isPresent()) {
+      opts << [
+        '-bottom',
+        """<!-- Matomo -->
+  <script>
+    var _paq = window._paq = window._paq || [];
+    /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
+    _paq.push(["setDoNotTrack", true]);
+    _paq.push(["disableCookies"]);
+    _paq.push(['trackPageView']);
+    _paq.push(['enableLinkTracking']);
+    (function() {
+      var u="https://analytics.apache.org/";
+      _paq.push(['setTrackerUrl', u+'matomo.php']);
+      _paq.push(['setSiteId', '85']);
+      var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
+      g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
+    })();
+  </script>
+  <!-- End Matomo Code -->${copyright}"""
+      ]
+    } else {
+      opts << [
+        '-bottom',
+        copyright
+      ]
+    }
 
     opts << [
       '-tag',