Implement topic alias management

[andsel]

Release notes

Implemented handling of topic alias received by publishers. Doesn't implement the alias remapping in forwarded publishes.

What does this PR do?

Updates CONNACK to set topic alias maximum property if user explicitly configures topic_alias_maximum configuration setting.
Adds a topic alias to topic name cache to MQTTConnection, named TopicAliasMapping.
Updates PUBLISH processing to handled the incoming topic alias, checking the various error condition (respect to the specification), resolve the alias to topic name and forward processing of publish message with topic name and without topic alias.
Added unit tests to MQTTConnection to cover the feature.

Why is it important/What is the impact to the user?

Implements the topic alias feature defined in the specification of MQTT 5. It handles only for incoming publishes, it doesn't apply any technique to replace topic names with aliases on the forward to subscribers phase.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works
• I have updated the Changelog if it's a feature or a fix that has to be reported

How to test this PR locally

Related issues

• Closes Topic alias support #859