Add missing assignment operators

Summary:
related to T13767
- add missing assignment operators
- marked single argument constructors as explicit where needed
- add even more missing includes

Reviewers: ivica

Reviewed By: ivica

Subscribers: iljazovic, miljen

Differential Revision: https://repo.mireo.local/D30813

include/async_mqtt5/mqtt_client.hpp

@@ -117,7 +117,7 @@ public:
 	 *
 	 * \details Moved-from client can only be destructed
 	 */
-	mqtt_client(mqtt_client&& other) noexcept = default;
+	mqtt_client(mqtt_client&&) noexcept = default;
 
 
 	/**