Added PGV constraint for serverName. (#12967)

Added PGV constraint to not allow

 in serverName.Currently, header doesn't allow
.

Risk Level: Low
Testing: config_test

Fixes #12709

Signed-off-by: Manish Kumar <manish.kumar1@india.nec.com>

Mirrored from https://github.com/envoyproxy/envoy @ 23df69ee53d0e0a68073885df27d8b893bd81eee

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

@@ -298,7 +298,8 @@ message HttpConnectionManager {
 
   // An optional override that the connection manager will write to the server
   // header in responses. If not set, the default is *envoy*.
-  string server_name = 10;
+  string server_name = 10
+      [(validate.rules).string = {well_known_regex: HTTP_HEADER_VALUE strict: false}];
 
   // Defines the action to be applied to the Server header on the response path.
   // By default, Envoy will overwrite the header with the value specified in

envoy/extensions/filters/network/http_connection_manager/v4alpha/http_connection_manager.proto

@@ -297,7 +297,8 @@ message HttpConnectionManager {
 
   // An optional override that the connection manager will write to the server
   // header in responses. If not set, the default is *envoy*.
-  string server_name = 10;
+  string server_name = 10
+      [(validate.rules).string = {well_known_regex: HTTP_HEADER_VALUE strict: false}];
 
   // Defines the action to be applied to the Server header on the response path.
   // By default, Envoy will overwrite the header with the value specified in