Feature: #95364 - Event to modify frontend user groups without authentication

See forge#95364

Description

Prior to TYPO3 v11, the "getGroupsFE" authentication service allowed to add and manipulate frontend user groups to be attached to a FrontendUserAuthentication request during runtime.

Extensions use this approach to attach certain properties for customization (for example country or region of a website user) dynamically for a specific request.

This functionality was removed during the refactoring of the authentication services (see forge#93108).

A new Event ModifyResolvedFrontendGroupsEvent has now been introduced to modify user groups, even if there is no authenticated user in place.

Impact

Use the new PSR-14 event to attach frontend user groups dynamically during a frontend request.