nixos/invoiceplane: Remove deprecated extraConfig

  nvimpager settings: user commands in `-c` and `--cmd` now override the

  respective default settings because they are executed later.

- The Invoiceplane module now only accepts the structured `settings` option.

  `extraConfig` is now removed.

- Legacy package `stalwart-mail_0_6` was dropped, please note the

  [manual upgrade process](https://github.com/stalwartlabs/mail-server/blob/main/UPGRADING.md)

  before changing the package to `pkgs.stalwart-mail` in

  extraConfig = hostName: cfg: let

    settings = mapAttrsToList (k: v: "${k}=${mkPhpValue v}") cfg.settings;

  in pkgs.writeText "extraConfig.php" ''

    ${concatStringsSep "\n" settings}

    ${toString cfg.extraConfig}

  '';

  in pkgs.writeText "extraConfig.php" (concatStringsSep "\n" settings);

  pkg = hostName: cfg: pkgs.stdenv.mkDerivation rec {

    pname = "invoiceplane-${hostName}";

          '';

        };

        extraConfig = mkOption {

          type = types.nullOr types.lines;

          default = null;

          example = ''

            SETUP_COMPLETED=true

            DISABLE_SETUP=true

            IP_URL=https://invoice.example.com

          '';

          description = ''

            InvoicePlane configuration. Refer to

            <https://github.com/InvoicePlane/InvoicePlane/blob/master/ipconfig.php.example>

            for details on supported values.

            **Note**: Please pass structured settings via

            `services.invoiceplane.sites.${name}.settings` instead, this option

            will get deprecated in the future.

          '';

        };

        settings = mkOption {

          type = types.attrsOf types.anything;

          default = {};

  # implementation

  config = mkIf (eachSite != {}) (mkMerge [{

    warnings = flatten (mapAttrsToList (hostName: cfg: [

      (optional (cfg.extraConfig != null) ''

        services.invoiceplane.sites."${hostName}".extraConfig will be deprecated in future releases, please use the settings option now.

      '')

    ]) eachSite);

    assertions = flatten (mapAttrsToList (hostName: cfg: [

      { assertion = cfg.database.createLocally -> cfg.database.user == user;

        message = ''services.invoiceplane.sites."${hostName}".database.user must be ${user} if the database is to be automatically provisioned'';