dfp: adding support for coalesced connections (#23521)

Unhiding a config option.

Testing: preexisting
Docs Changes: inline
Release Notes: inline

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

Mirrored from https://github.com/envoyproxy/envoy @ df48d99b0bc90fca5beb9f8fe4af45ebadeae80d

envoy/extensions/clusters/dynamic_forward_proxy/v3/cluster.proto

@@ -34,7 +34,6 @@ message ClusterConfig {
   // <envoy_v3_api_field_config.cluster.v3.Cluster.upstream_http_protocol_options>`
   bool allow_insecure_cluster_options = 2;
 
-  // [#not-implemented-hide:]
   // If true allow HTTP/2 and HTTP/3 connections to be reused for requests to different
   // origins than the connection was initially created for. This will only happen when the
   // resolved address for the new connection matches the peer address of the connection and
@@ -47,7 +46,6 @@ message ClusterConfig {
   //   By design, this feature will maximize reuse of connections. This means that instead
   //   opening a new connection when an existing connection reaches the maximum number of
   //   concurrent streams, requests will instead be sent to the existing connection.
-  //   TODO(alyssawilk) implement request queueing in connections.
   //
   // .. note::
   //   The coalesced connections might be to upstreams that would not be otherwise