fix: Fix Portlet preloading URL and Crossorigin - Meeds-io/meeds#2483

Prior to this change, the URL to preload when displaying the page is different from the loaded fetch call using JS services of the page layout. In addition, the crossorigin attribute has to be the same as the fetch call 'credentials' attribute which is with value 'include'.

layout-webapp/src/main/webapp/groovy/portal/webui/container/UIPageLayout.gtmpl

@@ -18,7 +18,7 @@
       def portletId = portlets.get(i).getId();
       if (portletId != null) {
         %>
-        <link rel="prefetch" as="fetch" type="text/html" href="<%=rcontext.getRequest().getRequestURI()%>?maximizedPortletId<%=portletId%>&showMaxWindow=true&hideSharedLayout=true&maximizedPortletMode=VIEW" crossorigin><%
+        <link rel="preload" as="fetch" href="<%=rcontext.getRequest().getRequestURI()%>?maximizedPortletId=<%=portletId%>&showMaxWindow=true&hideSharedLayout=true&maximizedPortletMode=VIEW" crossorigin="use-credentials"><%
       }
     }
   }