Resolves #712742 -
When Vehicle is offline and if any message needs to be sent then message gets Saved in offline Buffer collection. Once vehicle comes online then same message will be sent to vehicle. But in this message Kafka Headers are not sent which was part of original message.

Describe behaviour before the change

• Kafka Headers filed inside IgniteEvent were being ignored during serialization and de-serialization process, and thus were not being saved when storing the IgniteEvent in MongoDB.

Describe behaviour after the change

• KafkaHeaders filed in IgniteEvent instance will now be considered if non-null, during ser and de-ser.

Pull request checklist

• I have read the CONTRIBUTING.md
• My code follows the code style of this project
• Tests for the changes have been added (for bug fixes / features)
• All new and existing tests passed.
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

• Yes
• No