nixos/invoiceplane: Add settings option

- `services.knot` now supports `.settings` from RFC42.  The previous `.extraConfig` still works the same, but it displays a warning now.

- `services.invoiceplane` now supports .settings from RFC42. The previous .extraConfig still works the same, but it displays a warning now.

- `mu` now does not install `mu4e` files by default.  Users should get `mu4e` from Emacs lisp package set `emacs.pkgs.mu4e`.

- `mariadb` now defaults to `mariadb_1011` instead of `mariadb_106`, meaning the default version was upgraded from 10.6.x to 10.11.x. See the [upgrade notes](https://mariadb.com/kb/en/upgrading-from-mariadb-10-6-to-mariadb-10-11/) for potential issues.

    REMOVE_INDEXPHP=true

  '';

  extraConfig = hostName: cfg: pkgs.writeText "extraConfig.php" ''

  mkPhpValue = v:

    if isString v then escapeShellArg v

    # NOTE: If any value contains a , (comma) this will not get escaped

    else if isList v && any lib.strings.isCoercibleToString v then escapeShellArg (concatMapStringsSep "," toString v)

    else if isInt v then toString v

    else if isBool v then boolToString v

    else abort "The Invoiceplane config value ${lib.generators.toPretty {} v} can not be encoded."

  ;

  extraConfig = hostName: cfg: let

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

  in pkgs.writeText "extraConfig.php" ''

    ${concatStringsSep "\n" settings}

    ${toString cfg.extraConfig}

  '';

            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.

          '';

        };

        cron = {

        settings = mkOption {

          type = types.attrsOf types.anything;

          default = {};

          description = lib.mdDoc ''

            Structural InvoicePlane configuration. Refer to

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

            for details and supported values.

          '';

          example = literalExpression ''

            {

              SETUP_COMPLETED = true;

              DISABLE_SETUP = true;

              IP_URL = "https://invoice.example.com";

            }

          '';

        };

        cron = {

          enable = mkOption {

            type = types.bool;

            default = false;

              on how to configure it.

            '';

          };

          key = mkOption {

            type = types.str;

            description = lib.mdDoc "Cron key taken from the administration page.";

          };

        };

      };

  # implementation

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

    assertions = flatten (mapAttrsToList (hostName: cfg:

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

    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'';

      }

      { assertion = cfg.database.createLocally -> cfg.database.passwordFile == null;