The attribute of the metric in key value pair format.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v26/services/google_ads_service.proto)

| Fields ||
|---|---|
| ## `key` | `string` The key of the attribute. |
| ## `value` | `string` The value of the attribute. |