support STRUCT message keys

[deuscapturus]

Problem

There is currently no way to sink messages with composite keys without ignoring those keys.

Error "STRUCT is not supported as the document id."

https://github.com/confluentinc/kafka-connect-elasticsearch/issues/193

Solution

Convert message key STRUCT to a string for the doucment id.

Does this solution apply anywhere else?

• [ ] yes
• [ ] no

Test Strategy

unit test provided for DataConverter

Testing done:

• [x] Unit tests
• [ ] Integration tests
• [ ] System tests
• [ ] Manual tests

Release Plan

[ghost]

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[deuscapturus]

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[OneCricketeer]

I feel like a better solution is to just use a Transform on the Key

For example - https://jcustenborder.github.io/kafka-connect-documentation/projects/kafka-connect-transform-common/transformations/ToJSON.html