nixos/acme: also allow _PATH-suffixed credential files

The acmedns backend consumes a ACME_DNS_STORAGE_PATH environment
variable.

Upstream does treat this file as mutable (if you create or delete
accounts through the CLI, it would update it. We don't do this in our
module).

But the possibility for edits is probably why they didn't go with
`ACME_DNS_CONFIG` env var for the contents (as they'd be read-only), or
a `ACME_DNS_CONFIG_FILE`. (And the fact that a
`ACME_DNS_STORAGE_PATH_FILE` env var with questionable usability exists
is due to this logic being generic for most env vars).

So instead of fighting upstream over this, let's simply make our module
assertion also accept `_PATH` suffixes for `credentialFiles`.

Fixes #344684.

nixos/modules/security/acme/default.nix

@@ -826,8 +826,8 @@ let
           type = lib.types.attrsOf (lib.types.path);
           inherit (defaultAndText "credentialFiles" { }) default defaultText;
           description = ''
-            Environment variables suffixed by "_FILE" to set for the cert's service
-            for your selected dnsProvider.
+            Environment variables suffixed by "_FILE" or "_PATH" to set for the
+            cert's service for your selected dnsProvider.
             To find out what values you need to set, consult the documentation at
             <https://go-acme.github.io/lego/dns/> for the corresponding dnsProvider.
             This allows to securely pass credential files to lego by leveraging systemd
@@ -1186,10 +1186,13 @@ in
               }
             )
             {
-              assertion = lib.all (lib.hasSuffix "_FILE") (lib.attrNames data.credentialFiles);
+              assertion = lib.all (n: lib.hasSuffix "_FILE" n || lib.hasSuffix "_PATH" n) (
+                lib.attrNames data.credentialFiles
+              );
+
               message = ''
                 Option `security.acme.certs.${cert}.credentialFiles` can only be
-                used for variables suffixed by "_FILE".
+                used for variables suffixed by "_FILE" or "_PATH".
               '';
             }