nixos/ddclient: fewer passwords are supported in 21.11 than in 21.05

[Michcioperz]

Describe the bug

I was using ddclient with a strong randomly generated password and I migrated it to a passwordFile as part of the 21.11 upgrade. Ddclient didn't start after the upgrade.

Steps To Reproduce

Steps to reproduce the behavior:

1. Configure services.ddclient with passwordFile pointing at a file containing characters such as / followed by characters that aren't valid options for sed's s command such as o.
2. Rebuild.
3. Sed in prestart script of ddclient should choke on unknown option for s command.

Expected behavior

Ddclient starts despite non-alphanumeric chars in the passwordFile.

Notify maintainers

I don't know how to check maintainers for a module but I see @felschr did #143705

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[michcioperz@allison:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"aarch64-linux"`
 - host os: `Linux 5.10.81, NixOS, 21.11 (Porcupine)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.16`
 - channels(root): `"nixos-21.11.333896.a640d8394f3, nixos-21.05-21.05.4394.2553aee74fe, unstable-22.05pre335103.6daa4a5c045"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:
- ddclient