MQTTv5 CONNECT and PUBLISH implementation

[Pooja-Toshniwal]

Upgrading the library to support both v3.1.1 and v5.

Description

• This change adds the implementation of MQTT version 5 CONNECT, CONNACK, DISCONNECT, Outgoing PUBLISH and PUBLISH ACKS. To support the new features, version 5 is introduced.
• Existing data structures and functions are modified, and some new functions are added to serialize and deserialize the packets.
• New features will not affect the existing v3.1.1 functionalities as the new code is added with config variable MQTT_VERSION_5_ENABLED, which can be used to enable or disable version 5.
• For unit testing, the existing folder structure of test is modified to create a separate folder for v5.

Test Steps

• Unit tests added for all the modified and new functions added in mqttv5.

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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