Add API field in Router for Upstream Filters. (#23367)

Upstream filters specified in the router will apply if there are no filters specified in the cluster.

Risk Level: Low.
Testing: Unit and Integration testing.

Signed-off-by: Paul Gallagher <pgal@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 9bb570fded9246762d087c8d2c8fe9733ad0dbff

envoy/extensions/filters/http/router/v3/BUILD

@@ -7,6 +7,7 @@ licenses(["notice"])  # Apache 2
 api_proto_package(
     deps = [
         "//envoy/config/accesslog/v3:pkg",
+        "//envoy/extensions/filters/network/http_connection_manager/v3:pkg",
         "@com_github_cncf_udpa//udpa/annotations:pkg",
     ],
 )

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

@@ -3,6 +3,7 @@ syntax = "proto3";
 package envoy.extensions.filters.http.router.v3;
 
 import "envoy/config/accesslog/v3/accesslog.proto";
+import "envoy/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto";
 
 import "google/protobuf/wrappers.proto";
 
@@ -20,7 +21,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // Router :ref:`configuration overview <config_http_filters_router>`.
 // [#extension: envoy.filters.http.router]
 
-// [#next-free-field: 8]
+// [#next-free-field: 9]
 message Router {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.filter.http.router.v2.Router";
@@ -89,4 +90,20 @@ message Router {
   // :ref:`gRPC stats filter<config_http_filters_grpc_stats>` documentation
   // for more details.
   bool suppress_grpc_request_failure_code_stats = 7;
+
+  // .. note::
+  //   Upstream HTTP filters are currently in alpha.
+  //
+  // Optional HTTP filters for the upstream filter chain.
+  //
+  // These filters will be applied for all requests that pass through the router.
+  // They will also be applied to shadowed requests.
+  // Upstream filters cannot change route or cluster.
+  // Upstream filters specified on the cluster will override these filters.
+  //
+  // If using upstream filters, please be aware that local errors sent by
+  // upstream filters will not trigger retries, and local errors sent by
+  // upstream filters will count as a final response if hedging is configured.
+  // [#extension-category: envoy.filters.http.upstream]
+  repeated network.http_connection_manager.v3.HttpFilter upstream_http_filters = 8;
 }