Restrict SSR to paths in the sitemap

Because Angular SSR is not very efficient, after discussion with
the Google Scholar team we realized a compromise would be to only
use SSR for pages in the DSpace sitemap (and the home page).

(cherry picked from commit 5b3b3bfb9c)

server.ts

@@ -218,7 +218,7 @@ export function app() {
  * The callback function to serve server side angular
  */
 function ngApp(req, res, next) {
-  if (environment.ssr.enabled) {
+  if (environment.ssr.enabled && req.method === 'GET' && (req.path === '/' || environment.ssr.paths.some(pathPrefix => req.path.startsWith(pathPrefix)))) {
     // Render the page to user via SSR (server side rendering)
     serverSideRender(req, res, next);
   } else {