stackdriver: add cloud_logging_base_url docs

pipeline/outputs/stackdriver.md

@@ -36,6 +36,8 @@ Before to get started with the plugin configuration, make sure to obtain the pro
 | custom\_k8s\_regex | Set a custom regex to extract field like pod\_name, namespace\_name, container\_name and docker\_id from the local\_resource\_id in logs. This is helpful if the value of pod or node name contains dots. | `(?<pod_name>[a-z0-9](?:[-a-z0-9]*[a-z0-9])?(?:\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*)_(?<namespace_name>[^_]+)_(?<container_name>.+)-(?<docker_id>[a-z0-9]{64})\.log$` |
 | resource_labels | An optional list of comma separated strings specifying resource labels plaintext assignments (`new=value`) and/or mappings from an original field in the log entry to a destination field (`destination=$original`). Nested fields and environment variables are also supported using the [record accessor syntax](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/record-accessor). If configured, *all* resource labels will be assigned using this API only, with the exception of `project_id`. See [Resource Labels](#resource-labels) for more details. | |
 | compress | Set payload compression mechanism. The only available option is `gzip`. Default = "", which means no compression.|  |
+| cloud\_logging\_base\_url | Set the base Cloud Logging API URL to use for the /v2/entries:write API request. Default: https://logging.googleapis.com. |  |
+
 
 ### Configuration File