Fix documentation for TcpProxy.metadata_match (#36683)

Signed-off-by: Steven Jin Xuan <sjinxuan@microsoft.com>

Mirrored from https://github.com/envoyproxy/envoy @ ddbb15509be7c443873120a683f6992b45dfb326

envoy/extensions/filters/network/tcp_proxy/v3/tcp_proxy.proto

@@ -175,9 +175,9 @@ message TcpProxy {
   // :ref:`TcpProxy.weighted_clusters <envoy_v3_api_field_extensions.filters.network.tcp_proxy.v3.TcpProxy.weighted_clusters>`.
   OnDemand on_demand = 14;
 
-  // Optional endpoint metadata match criteria. Only endpoints in the upstream
-  // cluster with metadata matching that set in metadata_match will be
-  // considered. The filter name should be specified as ``envoy.lb``.
+  // Optional endpoint metadata match criteria used by the subset load balancer. Only endpoints
+  // in the upstream cluster with metadata matching what is set in this field will be considered
+  // for load balancing. The filter name should be specified as ``envoy.lb``.
   config.core.v3.Metadata metadata_match = 9;
 
   // The idle timeout for connections managed by the TCP proxy filter. The idle timeout