[Concept as discussed between Benni/Susi]
When a slug is updated by a user (by manually pressing the button), a redirect from the old URL to the new URL should be created.
After creation of the redirect a notification should be shown to the user. The notification should contain a link to remove the redirect again.
-> Update Slug
-> Auto-Create Redirect
-> Show Notification ("... created redirect... <Remove redirect>").
EXT:redirects is installed (Code should live in EXT:redirects)
Advanced use case:
When a user updates a slug of a page that has subpages, all subpage slugs starting with the current slug should also be updated and redirected. This batch operation should also be revertable via the notification.
* Redirects should have a defined life time (stop date) - for example 30 days (maybe make it configurable?)
* Behaviour should have a global enable/disable switch per site
* If the behaviour is enabled, redirects will be created and slugs updated independent of individual users rights to subpages, as otherwise inconsistent states are produced. If users should not be able to create redirects automatically, the behaviour has to be disabled.
* User rights are taken into account as the slug updates only happen if someone manually updates the slug of a page (and that only works if he/she has rights to the field)