nixos/grafana: disable preinstall when `declarativePlugins` is used

              type = types.bool;

            };

          };

          plugins = {

            preinstall_disabled = mkOption {

              description = ''

                When set to `true`, disables the Background Plugin Installer, which runs before Grafana starts.

                This component causes issues with `declarativePlugins` and is disabled by default if those are used.

              '';

              default = cfg.declarativePlugins != null;

              defaultText = literalExpression "cfg.declarativePlugins != null";

              type = types.bool;

            };

          };

        };

      };

    };