Follow-up from #1917
Give the user the ability to execute the "Remove & Retention" (aka smart remove) routine independent from running a snapshot. With this feature users can clean up existing backups based on their rules, e.g. after a new backup failed because of less storage space. This is needed because the remove-routine is executed after each backup, not before.
Could be a menu entry in "Backup" menu, named "Apply Remove- & Retention policy".