upstream: adding hidden config and creation for upstream filter facto… (#22544)

adding hidden config for upstream filters, and setting the cluster up to create upstream filters.
upstream filters are as yet unused, still cleaning up (#22434) but this makes it a much cleaner PR

(Also adding 2 random tweaks to router code because coverage was failing despite there previously being no changes to router code)

Risk Level: low (no-op if not configured)
Testing: unit tests
Docs Changes: n/a
Release Notes: n/a
part of #10455

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

Mirrored from https://github.com/envoyproxy/envoy @ 5261b4285d1487f93e7aece94786de9a8d3a2529

envoy/extensions/upstreams/http/v3/BUILD

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

envoy/extensions/upstreams/http/v3/http_protocol_options.proto

@@ -3,6 +3,7 @@ syntax = "proto3";
 package envoy.extensions.upstreams.http.v3;
 
 import "envoy/config/core/v3/protocol.proto";
+import "envoy/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto";
 
 import "udpa/annotations/status.proto";
 import "validate/validate.proto";
@@ -57,7 +58,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 //             http2_protocol_options:
 //               max_concurrent_streams: 100
 //        .... [further cluster config]
-// [#next-free-field: 6]
+// [#next-free-field: 7]
 message HttpProtocolOptions {
   // If this is used, the cluster will only operate on one of the possible upstream protocols.
   // Note that HTTP/2 or above should generally be used for upstream gRPC clusters.
@@ -148,4 +149,8 @@ message HttpProtocolOptions {
     // This allows switching on protocol based on ALPN
     AutoHttpConfig auto_config = 5;
   }
+
+  // [#not-implemented-hide:]
+  // Optional HTTP filters for the upstream filter chain.
+  repeated filters.network.http_connection_manager.v3.HttpFilter http_filters = 6;
 }