XWIKI-10027: Show date and time of the install and user who installed for an installed extension

* The ImportMojo should use the default Admin user to install extensions (otherwise we see "Installed by Unknown User").

xwiki-platform-tools/xwiki-platform-tool-packager-plugin/src/main/java/com/xpn/xwiki/tool/backup/ImportMojo.java

@@ -226,7 +226,8 @@ private void installExtension(Artifact artifact, XWikiContext xcontext, boolean
         extension.setFile(artifact.getFile());
 
         LocalExtension localExtension = localExtensionRepository.storeExtension(extension);
-        installedExtensionRepository.installExtension(localExtension, "wiki:xwiki", !directDependency);
+        installedExtensionRepository.installExtension(localExtension, "wiki:xwiki", !directDependency,
+            Collections.<String, Object>singletonMap("user.reference", "xwiki:XWiki.Admin"));
     }
 
     private MavenProject getMavenProject(Artifact artifact) throws MojoExecutionException