Add connection error codes

Summary:
related to T13651
- separate code related to reason codes into their own header
- introduce new connection error codes that will be return when a non-recoverable error occurs in connect_op
- add appropriate coverage tests

Reviewers: ivica

Reviewed By: ivica

Subscribers: miljen, iljazovic

Differential Revision: https://repo.mireo.local/D27808

include/async_mqtt5.hpp

@@ -4,6 +4,7 @@
 #include <async_mqtt5/error.hpp>
 #include <async_mqtt5/mqtt_client.hpp>
 #include <async_mqtt5/property_types.hpp>
+#include <async_mqtt5/reason_codes.hpp>
 #include <async_mqtt5/types.hpp>
 
 #endif // !ASYNC_MQTT5_HPP