ext_proc: convert ext_proc filter into dual filter (#33273)

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

Mirrored from https://github.com/envoyproxy/envoy @ 34bb97cfc9d22838c057f8ad0c18c7364024b8b1

envoy/service/ext_proc/v3/external_processor.proto

@@ -318,7 +318,8 @@ message CommonResponse {
 
   // Clear the route cache for the current client request. This is necessary
   // if the remote server modified headers that are used to calculate the route.
-  // This field is ignored in the response direction.
+  // This field is ignored in the response direction. This field is also ignored
+  // if the Envoy ext_proc filter is in the upstream filter chain.
   bool clear_route_cache = 5;
 }