manatee: Add sync ZFS dataset

hosts/manatee/disk-config.nix

@@ -172,6 +172,12 @@
               mountpoint = "/mnt/cameras";
               options.mountpoint = "legacy"; # otherwise we get a race between systemd and zfs; https://github.com/nix-community/disko/issues/214
             };
+
+            sync = {
+              type = "zfs_fs";
+              mountpoint = "/mnt/sync";
+              options.mountpoint = "legacy"; # otherwise we get a race between systemd and zfs; https://github.com/nix-community/disko/issues/214
+            };
           };
         };
       };