KIP-533 — Add default api timeout to AdminClient

Accepted Kafka 2.5 Admin

Adds a default.api.timeout.ms config to AdminClient that bounds the total wall-clock time for any admin operation including retries, with a per-operation override. Without it, AdminClient timeout semantics are controlled only by request.timeout.ms (per-attempt), making it impossible to reason about or bound the total time a single logical operation takes.

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