The ArcGISOnlineConnector supports paths to the service level for hosted feature services, but not to the layer level. To support managing sublayer metadata lets add support for Get Details and Set Details options to the layer path.
https://developers.arcgis.com/rest/services-reference/enterprise/fs-update-metadata/
https://<root>/<serviceName>/FeatureServer/<layerId>/metadata
https://<root>/<serviceName>/FeatureServer/<layerId>/metadata/update