Ext_proc: do not support fail_open+FULL_DUPLEX_STREAMED configuraton combination (#39740)

With FULL_DUPLEX_STREAMED mode, the fail open support is a little bit
tricky as there is no copy of body chunks stored in Envoy. Reject
FULL_DUPLEX_STREAMED+fail_open configuration combination for now.

---------

Signed-off-by: Yanjun Xiang <[email protected]>

Mirrored from https://github.com/envoyproxy/envoy @ 4861b2057afbc67290da0ec77ae1f1af60f152d0

Author: update-envoy[bot]

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

@@ -167,7 +167,11 @@ message ExternalProcessor {
     (xds.annotations.v3.field_status).work_in_progress = true
   ];
 
-  // By default, if the gRPC stream cannot be established, or if it is closed
+  // If the ``BodySendMode`` in the
+  // :ref:`processing_mode <envoy_v3_api_field_extensions.filters.http.ext_proc.v3.ExternalProcessor.processing_mode>`
+  // is set to ``FULL_DUPLEX_STREAMED``, ``failure_mode_allow`` can not be set to true.
+  //
+  // Otherwise, by default, if the gRPC stream cannot be established, or if it is closed
   // prematurely with an error, the filter will fail. Specifically, if the
   // response headers have not yet been delivered, then it will return a 500
   // error downstream. If they have been delivered, then instead the HTTP stream to the