nixos/dae: fix file location resolve

[oluceps]

Description of changes

Fix:
while specifying the subscription file like:

# config.dae
subscription {
    e: 'file://example'
}

It won't be found by the service:

"open /run/credentials/dae.service/example: no such file or directory"

Due to using the LoadCredentials mechanism.

The issue previous pr mentioned should not be an issue since /etc/ actually be managed by nix and not recommended manually edit.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[pokon548]

Result of nixpkgs-review pr 265270 run on x86_64-linux 1

2 packages blacklisted:

• nixos-install-tools
• tests.nixos-functions.nixos-test

[oluceps]

link daeuniverse/flake.nix#20

[oluceps]

outdated.

[oluceps]

For anyone who encounters issue with this module, try flake first.