tldr-update: init (#6401)

Adds `tldr-update` module for enabling automatic `tldr update` on a schedule.
Adds option to `tealdeer` to enable integration with new `tldr-update` module.

modules/services/tldr-update.nix

@@ -0,0 +1,50 @@
+{ config, lib, pkgs, ... }:
+let cfg = config.services.tldr-update;
+in {
+  meta.maintainers = [ lib.maintainers.perchun ];
+
+  options.services.tldr-update = {
+    enable = lib.mkEnableOption ''
+      Automatic updates for the tldr CLI
+    '';
+
+    package = lib.mkPackageOption pkgs "tldr" { example = "tlrc"; };
+
+    period = lib.mkOption {
+      type = lib.types.str;
+      default = "weekly";
+      description = ''
+        Systemd timer period to create for scheduled {command}`tldr --update`.
+
+        The format is described in {manpage}`systemd.time(7)`.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.user.services.tldr-update = {
+      Unit = {
+        Description = "Update tldr CLI cache";
+        Documentation = "https://tldr.sh/";
+      };
+
+      Service = {
+        Type = "oneshot";
+        ExecStart = ''
+          ${lib.getExe cfg.package} --update
+        '';
+      };
+    };
+
+    systemd.user.timers.tldr-update = {
+      Unit.Description = "Update tldr CLI cache";
+
+      Timer = {
+        OnCalendar = cfg.period;
+        Persistent = true;
+      };
+
+      Install.WantedBy = [ "timers.target" ];
+    };
+  };
+}