tcp proxy: enable to specify a path for HTTP tunneling with POST method (#24045)

Risk Level: low
Testing: unittest
Docs Changes: API doc
Release Notes: new feature
Fixes #24038

Signed-off-by: He Jie Xu <hejie.xu@intel.com>

Mirrored from https://github.com/envoyproxy/envoy @ ea2cdc3a164430ee43ff216655aaaac7fada51ed

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

@@ -64,6 +64,7 @@ message TcpProxy {
   // Configuration for tunneling TCP over other transports or application layers.
   // Tunneling is supported over both HTTP/1.1 and HTTP/2. Upstream protocol is
   // determined by the cluster configuration.
+  // [#next-free-field: 6]
   message TunnelingConfig {
     option (udpa.annotations.versioning).previous_message_type =
         "envoy.config.filter.network.tcp_proxy.v2.TcpProxy.TunnelingConfig";
@@ -103,6 +104,11 @@ message TcpProxy {
     // Save the response headers to the downstream info filter state for consumption
     // by the network filters. The filter state key is ``envoy.tcp_proxy.propagate_response_headers``.
     bool propagate_response_headers = 4;
+
+    // The path used with POST method. Default path is ``/``. If post path is specified and
+    // :ref:`use_post field <envoy_v3_api_field_extensions.filters.network.tcp_proxy.v3.TcpProxy.TunnelingConfig.use_post>`
+    // isn't true, it will be rejected.
+    string post_path = 5;
   }
 
   message OnDemand {