Update Inventory Notifications Settings

Updates inventory notification settings. * `channel_id` can be used as a query parameter to get inventory notification settings per channel. If omitted, you will interact with the global setting only. * Supplying `null` settings values per channel will delete overrides per given channel and values will be inherited from global level. * Partial updates are not supported within the given endpoint. In order to delete overrides per channel, `null` should be supplied for all the settings within...