nixos/xss-lock: add module (#40619)

`xsslock` (which was originally packaged in 6cb1d1aaaf02a72329bedf9c6960e54fea6f5c6e)
is a simple screensaver which connects a given screen locker (e.g.
`i3lock`) with `logind`. Whenever `loginctl lock-sessions` is invoked
the locker will be used to lock the screen. This works with its power
management features (e.g. `lid switch`) as well, so the PC can be locked
automatically when the lid is closed.

The module can be used like this:

```
{
  services.xserver.enable = true;

  programs.xss-lock.enable = true;
  programs.xss-lock.lockerCommand = "i3lock";
}
```

1 files changed, 1 insertions, 0 deletions

diff --git a/nixos/release.nix b/nixos/release.nix
index 4c0bb7bfb75..f7c2943b96f 100644
--- a/nixos/release.nix
+++ b/nixos/release.nix
@@ -402,6 +402,7 @@ in rec {
   tests.xfce = callTest tests/xfce.nix {};
   tests.xmonad = callTest tests/xmonad.nix {};
   tests.xrdp = callTest tests/xrdp.nix {};
+  tests.xss-lock = callTest tests/xss-lock.nix {};
   tests.yabar = callTest tests/yabar.nix {};
   tests.zookeeper = callTest tests/zookeeper.nix {};