fix: Support different consumer / producer configs

[benjackwhite]

Problem

We want to make migrating to a new kafka more straightfoward. Typically most of our services are consuming and then producing so if we want to migrate part-by-part what we really need is a way to specify a different producer to the consumer

Changes

• Added some new config options and made it so that every config can specify a target (consumer vs producer)
• Didn't do this for kafkajs as that is only used by consumers anyways (the default value)
• Refactored the producer code so that it is all in one place
• Added TODO for migrating replay to use this format (this can be our test bed on dev)

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Does this work well for both Cloud and self-hosted?

How did you test this code?