gphoto2: nixos programs module to configure udev

Closes #21420.

nixos/modules/programs/gphoto2.nix

@@ -0,0 +1,31 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  meta.maintainers = [ maintainers.league ];
+
+  ###### interface
+  options = {
+    programs.gphoto2 = {
+      enable = mkOption {
+        default = false;
+        example = true;
+        type = types.bool;
+        description = ''
+          Whether to configure system to use gphoto2.
+          To grant digital camera access to a user, the user must
+          be part of the camera group:
+          <code>users.extraUsers.alice.extraGroups = ["camera"];</code>
+        '';
+      };
+    };
+  };
+
+  ###### implementation
+  config = mkIf config.programs.gphoto2.enable {
+    services.udev.packages = [ pkgs.libgphoto2 ];
+    environment.systemPackages = [ pkgs.gphoto2 ];
+    users.extraGroups.camera = {};
+  };
+}