Additional Google Generated Customer Metadata, this field won't be provided by default and can be requested by setting the IncludeExtraData field in GetServiceRequest

A set of labels to apply to this service. Labels are key/value pairs that describe the service and all resources that belong to it (e.g., versions). The labels can be used to search and group resources, and are propagated to the usage and billing reports, enabling fine-grain analysis of costs. An example of using labels is to tag resources belonging to different environments (e.g., "env=prod", "env=qa"). Label keys and values can be no longer than 63 characters and can only contain lowercase letters, numeric characters, underscores, dashes, and international characters. Label keys must start with a lowercase letter or an international character. Each service can have at most 32 labels.