Ensure we can handle messages with empty payloads that have properties

[kellyfj]

NOTE: Working with folks at StreamNative to use this to validate behavior when a message is received with an empty payload but non-empty properties.

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Motivation

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Modifications

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Verifying this change

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This change is a trivial rework / code cleanup without any test coverage.

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This change is already covered by existing tests, such as (please describe tests).

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This change added tests and can be verified as follows:

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• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

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