KIP-1148 — Remove log.cleaner.enable and set lower bound 1 to log.cleaner.threads

Accepted Kafka 4.1 Broker

Deprecates `log.cleaner.enable` and removes it in Kafka 5.0, and sets a lower bound of 1 on `log.cleaner.threads`. The configuration is effectively a no-op since any compacted topic requires an active log cleaner; keeping it creates misleading silent failures (compaction silently stops) and unnecessary null-check complexity throughout the `LogCleaner`/`LogManager` code paths.

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