Implementaion of ext_proc filter disable immediate response (#28989)

This is implementation to address issue: #28698.

It's a follow up PR of #28907

Signed-off-by: Yanjun Xiang <yanjunxiang@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 00309b2db645d5ffba9f8e398f6fc9c21067b7c6

envoy/extensions/filters/http/ext_proc/v3/ext_proc.proto

@@ -205,7 +205,6 @@ message ExternalProcessor {
   // message in an external processor response. In such case, no local reply will be sent.
   // Instead, the stream to the external processor will be closed. There will be no
   // more external processing for this stream from now on.
-  // [#not-implemented-hide:]
   bool disable_immediate_response = 15;
 }