watchdog: init at 5.16

This is the Linux software `watchdog` as packaged on Debian, Raspbian,
and I believe Fedora. It has a number of configuration options not
available with the systemd watchdog, including rebooting if unable to
ping a specific host, if a specific network adapter fails, and can also
perform custom tests and actions.

pkgs/by-name/wa/watchdog/package.nix

···
+{
+  lib,
+  stdenv,
+  fetchzip,
+}:
+stdenv.mkDerivation (finalAttrs: {
+  version = "5.16";
+  pname = "watchdog";
+  src = fetchzip {
+    url = "mirror://sourceforge/watchdog/watchdog-${finalAttrs.version}.tar.gz";
+    hash = "sha256-ecXsnPvAhlRB8jiTgK+i1j6m/0idNqmzjSqi6UGCydE=";
+  };
+  makeFlags = [
+    "CONFIG_FILENAME:=${placeholder "out"}/etc/watchdog.conf"
+  ];
+
+  meta = {
+    description = "Software watchdog for Linux";
+    homepage = "https://sourceforge.net/projects/watchdog/";
+    license = lib.licenses.gpl2;
+    platforms = lib.platforms.linux;
+    maintainers = with lib.maintainers; [ n8henrie ];
+    mainProgram = "watchdog";
+  };
+})