nixos/glance: add environmentFile option

        attribute set with this format: `{ _secret = "/path/to/secret"; }`.

        See the example in `services.glance.settings.pages` at the weather widget

        with a location secret to get a better picture of this.

        Alternatively, you can use a single file with environment variables,

        see `services.glance.environmentFile`.

      '';

    };

    environmentFile = mkOption {

      type = types.nullOr types.path;

      description =

        let

          singleQuotes = "''";

        in

        ''

          Path to an environment file as defined in {manpage}`systemd.exec(5)`.

          See upstream documentation

          <https://github.com/glanceapp/glance/blob/main/docs/configuration.md#environment-variables>.

          Example content of the file:

          ```

          TIMEZONE=Europe/Paris

          ```

          Example `services.glance.settings.pages` configuration:

          ```nix

            [

              {

                name = "Home";

                columns = [

                  {

                    size = "full";

                    widgets = [

                      {

                        type = "clock";

                        timezone = "\''${TIMEZONE}";

                        label = "Local Time";

                      }

                    ];

                  }

                ];

              }

            ];

          ```

          Note that when using Glance's `''${ENV_VAR}` syntax in Nix,

          you need to escape it as follows: use `\''${ENV_VAR}` in `"` strings

          and `${singleQuotes}''${ENV_VAR}` in `${singleQuotes}` strings.

          Alternatively, you can put each secret in it's own file,

          see `services.glance.settings`.

        '';

      default = "/dev/null";

      example = "/var/lib/secrets/glance";

    };

    openFirewall = mkOption {

          '';

        ExecStart = "${getExe cfg.package} --config ${mergedSettingsFile}";

        WorkingDirectory = "/var/lib/glance";

        EnvironmentFile = cfg.environmentFile;

        StateDirectory = "glance";

        RuntimeDirectory = "glance";

        RuntimeDirectoryMode = "0755";