Feature/preserve case support formatter on unknown headers (#20780)

Signed-off-by: jiangshantao <jiangshantao-dbg@qq.com>

Mirrored from https://github.com/envoyproxy/envoy @ 496d9103b1de1496daf7d0ee29e7ff204726c7eb

envoy/extensions/http/header_formatters/preserve_case/v3/preserve_case.proto

@@ -3,6 +3,7 @@ syntax = "proto3";
 package envoy.extensions.http.header_formatters.preserve_case.v3;
 
 import "udpa/annotations/status.proto";
+import "validate/validate.proto";
 
 option java_package = "io.envoyproxy.envoy.extensions.http.header_formatters.preserve_case.v3";
 option java_outer_classname = "PreserveCaseProto";
@@ -17,7 +18,22 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // See the :ref:`header casing <config_http_conn_man_header_casing>` configuration guide for more
 // information.
 message PreserveCaseFormatterConfig {
+  enum FormatterTypeOnEnvoyHeaders {
+    // Use LowerCase on Envoy added headers.
+    DEFAULT = 0;
+
+    // Use ProperCaseHeaderKeyFormatter on Envoy added headers that upper cases the first character
+    // in each word. The first character as well as any alpha character following a special
+    // character is upper cased.
+    PROPER_CASE = 1;
+  }
+
   // Allows forwarding reason phrase text.
   // This is off by default, and a standard reason phrase is used for a corresponding HTTP response code.
   bool forward_reason_phrase = 1;
+
+  // Type of formatter to use on headers which are added by Envoy (which are lower case by default).
+  // The default type is DEFAULT, use LowerCase on Envoy headers.
+  FormatterTypeOnEnvoyHeaders formatter_type_on_envoy_headers = 2
+      [(validate.rules).enum = {defined_only: true}];
 }