fix broken envoy docs link (#2937)

Author: rsalmond

mesh/v1alpha1/istio.mesh.v1alpha1.pb.html

@@ -274,7 +274,7 @@ message Topology {
 
 // ForwardClientCertDetails controls how the x-forwarded-client-cert (XFCC)
 // header is handled by the gateway proxy.
-// See [Envoy XFCC](https://www.envoyproxy.io/docs/envoy/latest/api-v2/config/filter/network/http_connection_manager/v2/http_connection_manager.proto#envoy-api-enum-config-filter-network-http-connection-manager-v2-httpconnectionmanager-forwardclientcertdetails)
+// See [Envoy XFCC](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto.html#enum-extensions-filters-network-http-connection-manager-v3-httpconnectionmanager-forwardclientcertdetails)
 // header handling for more details.
 enum ForwardClientCertDetails {
   // Field is not set