network: reintroduce #4382 (delayed conn close) with segv fix (#4587)

Re-enable the changes reverted in 9d32e5c2a14cd9ab96b6e77fb04f7bd77b2c0d71, which were originally merged as part of #4382.

Signed-off-by: Andres Guedez <aguedez@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ b16f5299e45ca71a36ec6f7fc006ed311b58a843

envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto

@@ -175,7 +175,6 @@ message HttpConnectionManager {
   // option is not specified.
   google.protobuf.Duration drain_timeout = 12 [(gogoproto.stdduration) = true];
 
-  // [#not-implemented-hide:]
   // The delayed close timeout is for downstream connections managed by the HTTP connection manager.
   // It is defined as a grace period after connection close processing has been locally initiated
   // during which Envoy will flush the write buffers for the connection and await the peer to close