[ticket/14462] Further speed improvements

- Cache the secondary container
- Only initialize tasks/modules that are being used
- Add timeout error message in the AJAX UI

PHPBB3-14462

phpBB/config/installer/container/services_install_controller.yml

@@ -53,6 +53,7 @@ services:
     phpbb.installer.controller.convert:
         class: phpbb\convert\controller\convertor
         arguments:
+            - '@cache.driver'
             - '@installer.helper.container_factory'
             - '@installer.helper.database'
             - '@phpbb.installer.controller.helper'