nixos/incus: add zfs/lib/udev to path

Incus needs to find zvol_id for some operations, but zfs does not put
this executable in the bin directory. Exposing lib/udev into the Incus
path solves discovery of the executable

https://github.com/lxc/incus/blob/e5690705e842d3961d8a1d18c0ec002c25345af8/internal/server/storage/drivers/driver_zfs_volumes.go#L1820C1-L1820C41
(cherry picked from commit 7585f26)

nixos/modules/virtualisation/incus.nix

@@ -158,7 +158,10 @@ in
         "network-online.target"
       ];
 
-      path = lib.mkIf config.boot.zfs.enabled [ config.boot.zfs.package ];
+      path = lib.mkIf config.boot.zfs.enabled [
+        config.boot.zfs.package
+        "${config.boot.zfs.package}/lib/udev"
+      ];
 
       environment = {
         # Override Path to the LXC template configuration directory