MDL-82297 core: Add notification to warn admins

* In Moodle 5.0 we will remove Chat and Survey module
and we will need to announce it beforehand

admin/renderer.php

@@ -295,6 +295,7 @@ class core_admin_renderer extends plugin_renderer_base {
 
         $output .= $this->header();
         $output .= $this->output->heading(get_string('notifications', 'admin'));
+        $output .= $this->upgrade_news_message();
         $output .= $this->maturity_info($maturity);
         $output .= empty($CFG->disableupdatenotifications) ? $this->available_updates($availableupdates, $availableupdatesfetch) : '';
         $output .= $this->insecure_dataroot_warning($insecuredataroot);
@@ -754,6 +755,22 @@ class core_admin_renderer extends plugin_renderer_base {
         return $this->box($copyrighttext, 'copyright');
     }
 
+    /**
+     * Display a transient notification for important upgrades messages for
+     * specific releases.
+     *
+     * @return string HTML to output.
+     */
+    protected function upgrade_news_message() {
+        return $this->notification(
+            get_string('importantupdates_content', 'admin'),
+            'info',
+            false,
+            get_string('importantupdates_title', 'admin'),
+            'i/circleinfo, core'
+        );
+    }
+
     /**
      * Display a warning about installing development code if necesary.
      * @param int $maturity