gpg: allow for duplicate keys in config (#1814)

Allow for duplicate keys in the form of a list of strings.

Also update the `settings` example configuration to use `literalExample`.

tests/modules/programs/gpg/override-defaults-expected.conf

@@ -14,6 +14,8 @@ require-cross-certification
 s2k-cipher-algo AES128
 s2k-digest-algo SHA512
 throw-keyids
+trusted-key 0xXXXXXXXXXXXXX
+trusted-key 0xYYYYYYYYYYYYY
 use-agent
 verify-options show-uid-validity
-with-fingerprint
+with-fingerprint

tests/modules/programs/gpg/override-defaults.nix

@@ -11,6 +11,10 @@ with lib;
         no-comments = false;
         s2k-cipher-algo = "AES128";
         throw-keyids = true;
+        trusted-key = [
+          "0xXXXXXXXXXXXXX"
+          "0xYYYYYYYYYYYYY"
+        ];
       };
     };