KafkaBufferIT tests for writeBytes

[dlvenable]

Description

This PR follows on after #3635 with some integration test improvements.

• Adds a test case to verify that raw bytes are wrapped in the Protobuf message.
• Adds a test case to verify that raw bytes are wrapped in the Protobuf message and encrypted when encryption is configured.
• Verifies the Event received after calling writeBytes. This adds a verification to an existing test case that should have been there.
• Some test naming improvements
• Adding final modifiers.

Issues Resolved

N/A

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

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[dlvenable]

@kkondaka , Please take a look and see if the new tests address your concerns from this comment. #3635 (comment)