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• What impact (if any) will there be on existing users? Deprecating it in StreamsConfig  shouldn't impact current users negatively: 

• If we are changing behavior how will we phase out the older behavior? We should change the config docs first to deprecate. In the future, remove the configuration could be called for. See https://github.com/apache/kafka/pull/14360 for a PR in progress, as well as a discussion of this issue.
• If we need special migration tools, describe them here.
• When will we remove the existing behavior? Post docs change and deprecation, for major release 5. 

Test Plan

should not impact tests directly

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