add eds service_name to LoadStats proto and populate it in LRS request (#6028)

This new field gives LRS management server the extra info that two clusters may be using the same set of hosts to serve, and it's the management server's call whether to aggregate on the clusterStats.

Risk Level: LOW (new field)
Testing: unit test

Fixes #5986

Signed-off-by: Xin Zhuang <stevenzzz@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ f5bb174c5f2f598df497cec04b0e144af9612570

envoy/api/v2/endpoint/load_report.proto

@@ -117,10 +117,16 @@ message EndpointLoadMetricStats {
 // Per cluster load stats. Envoy reports these stats a management server in a
 // :ref:`LoadStatsRequest<envoy_api_msg_load_stats.LoadStatsRequest>`
 // [#not-implemented-hide:] Not configuration. TBD how to doc proto APIs.
+// Next ID: 7
 message ClusterStats {
   // The name of the cluster.
   string cluster_name = 1 [(validate.rules).string.min_bytes = 1];
 
+  // The eds_cluster_config service_name of the cluster.
+  // It's possible that two clusters send the same service_name to EDS,
+  // in that case, the management server is supposed to do aggregation on the load reports.
+  string cluster_service_name = 6;
+
   // Need at least one.
   repeated UpstreamLocalityStats upstream_locality_stats = 2
       [(validate.rules).repeated .min_items = 1];