Add script to move a backup to another server
i.e. send the ZFS, update db records and copy the config files. The sql inserts should broadly mirror those done when setting up a new backup, though with field values matching those in the source database rather than just using the defaults. This script has so only been tested for the case of moving a "simple" backup where a host has a single backup task and no special config. It's quite likely there'll be bugs to fix for other cases that we'll find in due course.