add metrics service config example (#17464)

Commit Message: add metrics service config example
Additional Description:
Risk Level:
Testing:
Docs Changes: add metrics service config example

Signed-off-by: JaredTan95 <jian.tan@daocloud.io>

Mirrored from https://github.com/envoyproxy/envoy @ ea9a80627a9aa6fa7887b4501015d29933ff9b78

envoy/config/metrics/v3/metrics_service.proto

@@ -21,6 +21,17 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // Metrics Service is configured as a built-in *envoy.stat_sinks.metrics_service* :ref:`StatsSink
 // <envoy_v3_api_msg_config.metrics.v3.StatsSink>`. This opaque configuration will be used to create
 // Metrics Service.
+//
+// Example:
+//
+// .. code-block:: yaml
+//
+//     stats_sinks:
+//       - name: envoy.stat_sinks.metrics_service
+//         typed_config:
+//           "@type": type.googleapis.com/envoy.config.metrics.v3.MetricsServiceConfig
+//           transport_api_version: V3
+//
 // [#extension: envoy.stat_sinks.metrics_service]
 message MetricsServiceConfig {
   option (udpa.annotations.versioning).previous_message_type =