nixos/maddy: add package option (#396535)

nixos/modules/services/mail/maddy.nix

···
 
       enable = lib.mkEnableOption "Maddy, a free an open source mail server";
 
+      package = lib.mkPackageOption pkgs "maddy" { };
+
       user = lib.mkOption {
         default = "maddy";
         type = with lib.types; uniq str;
···
 
     systemd = {
 
-      packages = [ pkgs.maddy ];
+      packages = [ cfg.package ];
       services = {
         maddy = {
           serviceConfig = {
···
           script = ''
             ${lib.optionalString (cfg.ensureAccounts != [ ]) ''
               ${lib.concatMapStrings (account: ''
-                if ! ${pkgs.maddy}/bin/maddyctl imap-acct list | grep "${account}"; then
-                  ${pkgs.maddy}/bin/maddyctl imap-acct create ${account}
+                if ! ${cfg.package}/bin/maddyctl imap-acct list | grep "${account}"; then
+                  ${cfg.package}/bin/maddyctl imap-acct create ${account}
                 fi
               '') cfg.ensureAccounts}
             ''}
             ${lib.optionalString (cfg.ensureCredentials != { }) ''
               ${lib.concatStringsSep "\n" (
-                lib.mapAttrsToList (name: cfg: ''
-                  if ! ${pkgs.maddy}/bin/maddyctl creds list | grep "${name}"; then
-                    ${pkgs.maddy}/bin/maddyctl creds create --password $(cat ${lib.escapeShellArg cfg.passwordFile}) ${name}
+                lib.mapAttrsToList (name: credentials: ''
+                  if ! ${cfg.package}/bin/maddyctl creds list | grep "${name}"; then
+                    ${cfg.package}/bin/maddyctl creds create --password $(cat ${lib.escapeShellArg credentials.passwordFile}) ${name}
                   fi
                 '') cfg.ensureCredentials
               )}
···
     };
 
     environment.systemPackages = [
-      pkgs.maddy
+      cfg.package
     ];
   };
 }