Gracefully shutdown Websocket and TLS streams

Summary:
Resolves #18
Ref T15241

Reviewers: ivica

Reviewed By: ivica

Subscribers: korina, miljen

Maniphest Tasks: T15241

Differential Revision: https://repo.mireo.local/D33395

example/hello_world_over_tls.cpp

@@ -9,6 +9,7 @@
 #include <boost/mqtt5/logger.hpp>
 #include <boost/mqtt5/mqtt_client.hpp>
 #include <boost/mqtt5/types.hpp>
+#include <boost/mqtt5/ssl.hpp> // OpenSSL traits
 
 #include <boost/asio/detached.hpp>
 #include <boost/asio/io_context.hpp>