watson: add module

Watson is a CLI for tracking your time.

Two unit tests were added to validate the module behavior for an empty
configuration and the example configuration.

tests/modules/programs/watson/example-settings.nix

@@ -0,0 +1,40 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  programs.watson = {
+    enable = true;
+    package = config.lib.test.mkStubPackage { };
+
+    settings = {
+      backend = {
+        url = "https://api.crick.fr";
+        token = "yourapitoken";
+      };
+
+      options = {
+        stop_on_start = true;
+        stop_on_restart = false;
+        date_format = "%Y.%m.%d";
+        time_format = "%H:%M:%S%z";
+        week_start = "monday";
+        log_current = false;
+        pager = true;
+        report_current = false;
+        reverse_log = true;
+      };
+    };
+  };
+
+  nmt.script = let
+    configDir = if pkgs.stdenv.hostPlatform.isDarwin then
+      "home-files/Library/Application Support"
+    else
+      "home-files/.config";
+  in ''
+    assertFileContent \
+      "${configDir}/watson/config" \
+      ${./example-settings-expected.ini}
+  '';
+}