grpc-proxy: listenAddr/metrics exposes metrics of proxy -> endpoint not etcd server endpoint.

[hexfusion]

etcd grpc-proxy --listen-addr HandleHealth handler returns /health of the endpoint but HandlePrometheus /metrics endpoint returns metrics of the proxy itself. I feel this is a bug. We have a separate flag to expose proxy metrics --metrics-addr.

etcd/etcdmain/grpc_proxy.go

Lines 328 to 332 in 627cffd

	func mustHTTPListener(m cmux.CMux, tlsinfo *transport.TLSInfo, c *clientv3.Client) (*http.Server, net.Listener) {
	httpmux := http.NewServeMux()
	httpmux.HandleFunc("/", http.NotFound)
	etcdhttp.HandlePrometheus(httpmux)
	grpcproxy.HandleHealth(httpmux, c)