KIP-1362 — Add a rollback-compatible storage format option for KRaft migration

Discussion KRaftBroker

Adds an optional flag to `kafka-storage.sh format` that writes a rollback-compatible `meta.properties` with version=0 instead of unconditionally writing version=1. Replacing a failed broker mid-migration using the documented provisioning procedure silently destroys the ZooKeeper rollback capability, because the replacement crashes on its own storage once the cluster is put back into migration mode.

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