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

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api