Fix out of order PUBACK and PUBLISH handling

[aggarg]

Description

The current implementation uses task notification to wait for acknowledgements and incoming publishes and therefore, cannot differentiate between acknowledgements and incoming publishes. This causes a crash when an incoming PUBLISH is received before PUBACK for the previous outgoing publish.

This PR uses an event group to wait for acknowledgements and incoming publishes. This allows us to differentiate between acknowledgements and incoming publishes by waiting for different bits.

Test Steps

Run pub-sub demo:

 (9822) sub_pub_unsub_demo: coreMQTT-Agent connected.
I (9832) core_mqtt_agent_manager: coreMQTT-Agent connected.
I (9842) sub_pub_unsub_demo: Task "SubPub0" sending subscribe request to coreMQTT-Agent for topic filter: /filter/SubPub0 with id 1
I (9852) sub_pub_unsub_demo: Task "SubPub1" sending subscribe request to coreMQTT-Agent for topic filter: /filter/SubPub1 with id 2
I (10542) sub_pub_unsub_demo: Subscribe 1 for topic filter /filter/SubPub0 succeeded for task "SubPub0".
I (10542) sub_pub_unsub_demo: Task "SubPub0" sending publish request to coreMQTT-Agent with message "SubPub0" on topic "/filter/SubPub0" with ID 3.
I (10552) sub_pub_unsub_demo: Task "SubPub0" waiting for publish 3 to complete.
I (12212) sub_pub_unsub_demo: Subscribe 2 for topic filter /filter/SubPub1 succeeded for task "SubPub1".
I (12222) sub_pub_unsub_demo: Task "SubPub1" sending publish request to coreMQTT-Agent with message "SubPub1" on topic "/filter/SubPub1" with ID 4.
I (12232) sub_pub_unsub_demo: Task "SubPub1" waiting for publish 4 to complete.
I (14212) coreMQTT: Publishing message to /filter/SubPub0.

I (15212) coreMQTT: Publishing message to /filter/SubPub1.

I (17002) coreMQTT: Ack packet deserialized with result: MQTTSuccess.
I (17002) coreMQTT: State record updated. New state=MQTTPublishDone.
I (17002) coreMQTT: Ack packet deserialized with result: MQTTSuccess.
I (17012) coreMQTT: State record updated. New state=MQTTPublishDone.
I (17022) coreMQTT: De-serialized incoming PUBLISH packet: DeserializerResult=MQTTSuccess.
I (17022) coreMQTT: State record updated. New state=MQTTPubAckSend.
I (17032) coreMQTT: De-serialized incoming PUBLISH packet: DeserializerResult=MQTTSuccess.
I (17042) coreMQTT: State record updated. New state=MQTTPubAckSend.
I (17052) sub_pub_unsub_demo: Publish 3 succeeded for task "SubPub0".
I (17052) sub_pub_unsub_demo: Task "SubPub0" received: SubPub0
I (17062) sub_pub_unsub_demo: Task "SubPub0" sending unsubscribe request to coreMQTT-Agent for topic filter: /filter/SubPub0 with id 5
I (17062) sub_pub_unsub_demo: Publish 4 succeeded for task "SubPub1".
I (17082) sub_pub_unsub_demo: Task "SubPub1" received: SubPub1
I (17092) sub_pub_unsub_demo: Task "SubPub1" sending unsubscribe request to coreMQTT-Agent for topic filter: /filter/SubPub1 with id 6
I (19652) sub_pub_unsub_demo: Unsubscribe 5 for topic filter /filter/SubPub0 succeeded for task "SubPub0".
I (19652) sub_pub_unsub_demo: Task "SubPub0" completed a loop. Delaying before next loop.
I (21292) sub_pub_unsub_demo: Unsubscribe 6 for topic filter /filter/SubPub1 succeeded for task "SubPub1".
I (21292) sub_pub_unsub_demo: Task "SubPub1" completed a loop. Delaying before next loop.

Checklist:

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

Related Issue

#63

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