KIP-597 — MirrorMaker2 internal topics Formatters

Accepted Kafka 2.7 MirrorMaker

Adds a `MirrorMaker2MessageFormatter` that decodes and pretty-prints records from MirrorMaker 2 internal topics (`mm2-offsets`, `mm2-configs`, `mm2-status`) so their binary content can be inspected via `kafka-console-consumer`. MirrorMaker 2 internal topics use binary encoding with no existing formatter, making debugging offset or configuration issues require custom decoding tools.

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