swaylock: accept path type for settings values

[GaetanLepage]

Description

Currently, path values are not accepted as programs.swaylock.settings values:

error: A definition for option `home-manager.users.gaetan.programs.swaylock.settings.image' is not of type `boolean or floating point number or signed integer or string'.

This would allow for:

programs.swaylock = {
  enable = true;

  settings.image = ./wallpaper.png;
};

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all
  or nix build --reference-lock-file flake.lock ./tests#test-all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

cc @rcerc