[grpc-transcoder] Add option to pack unknown parameters into HttpBody extension (#34999)

Commit Message: [grpc-transcoder] Add option to pack unknown parameters
into HttpBody extension
Additional Description: We've been using this behavior for years, with
PR #15338 as a patch. Finally getting around to trying to upstream the
behavior to make it available for others, and to make it so I don't have
to keep repositioning the patch. Unlike #15338 I'm also adding a
configuration option so that no behavior change will occur without a
corresponding configuration change.
Risk Level: Very low, guarded by a new config field.
Testing: Added positive unit tests, added conditions to other tests for
the negative case.
Docs Changes: Autogen
Fixes #14710

---------

Signed-off-by: Raven Black <ravenblack@dropbox.com>

Mirrored from https://github.com/envoyproxy/envoy @ f837c480adad94e8d1a05ef648c26ffce7ecd286

envoy/extensions/filters/http/grpc_json_transcoder/v3/transcoder.proto

@@ -18,7 +18,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // gRPC-JSON transcoder :ref:`configuration overview <config_http_filters_grpc_json_transcoder>`.
 // [#extension: envoy.filters.http.grpc_json_transcoder]
 
-// [#next-free-field: 17]
+// [#next-free-field: 18]
 // GrpcJsonTranscoder filter configuration.
 // The filter itself can be used per route / per virtual host or on the general level. The most
 // specific one is being used for a given route. If the list of services is empty - filter
@@ -88,7 +88,8 @@ message GrpcJsonTranscoder {
     // When set to true, the request will be rejected with a ``HTTP 400 Bad Request``.
     //
     // The fields
-    // :ref:`ignore_unknown_query_parameters <envoy_v3_api_field_extensions.filters.http.grpc_json_transcoder.v3.GrpcJsonTranscoder.ignore_unknown_query_parameters>`
+    // :ref:`ignore_unknown_query_parameters <envoy_v3_api_field_extensions.filters.http.grpc_json_transcoder.v3.GrpcJsonTranscoder.ignore_unknown_query_parameters>`,
+    // :ref:`capture_unknown_query_parameters <envoy_v3_api_field_extensions.filters.http.grpc_json_transcoder.v3.GrpcJsonTranscoder.capture_unknown_query_parameters>`,
     // and
     // :ref:`ignored_query_parameters <envoy_v3_api_field_extensions.filters.http.grpc_json_transcoder.v3.GrpcJsonTranscoder.ignored_query_parameters>`
     // have priority over this strict validation behavior.
@@ -288,4 +289,20 @@ message GrpcJsonTranscoder {
   //
   // If unset, the current stream buffer size is used.
   google.protobuf.UInt32Value max_response_body_size = 16 [(validate.rules).uint32 = {gt: 0}];
+
+  // If true, query parameters that cannot be mapped to a corresponding
+  // protobuf field are captured in an HttpBody extension of UnknownQueryParams.
+  bool capture_unknown_query_parameters = 17;
+}
+
+// ``UnknownQueryParams`` is added as an extension field in ``HttpBody`` if
+// ``GrpcJsonTranscoder::capture_unknown_query_parameters`` is true and unknown query
+// parameters were present in the request.
+message UnknownQueryParams {
+  message Values {
+    repeated string values = 1;
+  }
+
+  // A map from unrecognized query parameter keys, to the values associated with those keys.
+  map<string, Values> key = 1;
 }