fix(kafka): handle tombstone events without value

[haslers]

Summary

The Kafka consumer was failing when processing messages with undefined values because the value getter attempted to deserialize undefined values, causing a TypeError when fromBase64 tried to access the length property of undefined.

Changes

Fixed the issue by adding an undefined check to the value getter in the consumer.
When a tombstone event without a message (i.e, value is undefined) is encountered, the consumer now properly returns undefined instead of throwing an error.

Updated type definitions to allow undefined values in the deserialization chain and added comprehensive test coverage for undefined value scenarios.

Issue number: closes #5016

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[boring-cyborg]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!