Fix EZP-22609: Access to /user/login should redirect to new login resource

https://jira.ez.no/browse/EZP-22609

This patch safely redirects a user requesting access to legacy login (`/user/login`) to the new login resource (`/login`).
Note that siteaccesses in legacy mode will not be concerned as the newly created route (`_ezpublishLegacyLogin`) is not declared as *legacy aware*.

`/user/logout` is also taken into account.