[KafkaIO] Replace end offset consumer with admin client

[sjvanrossum]

Continuing from #36075, this PR removes support for old Kafka client libraries, requiring at least Kafka 2.8.2 or newer. Note that every version of Kafka <4.0.0 still supports API protocol versions <0.10.0 and the compatibility matrix indicates that versions of Kafka >=3.0.0 would provide the best compatibility in combination with versions of Kafka >=4.0.0.

I've got another change to the poll loop queued up that leverages features only available in versions of Kafka >=3.0.0, so I'll address that compatibility bit in a following PR.

This PR leverages the Admin client to request end offsets without creating buffers like Consumer clients do. Profiling showed that Admin clients used 10% of the memory that was used by Consumer clients for end offset requests. The Admin client returns a KafkaFuture for every request which is fulfilled by an IO thread managed by the Kafka client library, thus restoring the background thread feature that was removed in #36075.

I intend to backport this change to KafkaUnboundedReader in a separate PR.

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Summary of Changes

Hello @sjvanrossum, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request modernizes the KafkaIO connector by upgrading the minimum supported Kafka client version and refactoring how end offsets are retrieved. By switching from the Consumer client to the more efficient Admin client for offset requests, the change significantly improves memory performance and reintroduces asynchronous background processing for these operations. This update ensures better resource utilization and aligns the connector with more recent Kafka client capabilities.

Highlights

• Kafka Version Upgrade: The minimum required Kafka client library version has been updated to 2.8.2 or newer, removing support for older versions (2.0.1, 2.3.1, 2.4.1, 2.5.1).
• Memory Efficiency Improvement: The KafkaIO connector now leverages the Kafka Admin client instead of the Consumer client for requesting end offsets. This change significantly reduces memory usage, with profiling showing a 90% reduction for end offset requests.
• Restored Background Thread Feature: The Admin client returns a KafkaFuture for each request, which is fulfilled by an I/O thread managed by the Kafka client library. This restores the background thread feature for offset requests that was previously removed.
• API Modernization: New methods like withAdminFactoryFn have been added to KafkaIO.Read and KafkaIO.ReadSourceDescriptors to allow users to provide a custom Admin client factory, enhancing flexibility and supporting different Kafka Admin versions.

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[sjvanrossum]

Note that this change may break KafkaIO configurations with complex Consumer factories. A Consumer factory should not be used to alter the environment (a JvmInitializer is more fitting) or configuration (a configuration supplier property should be added). I'm actually thinking we should keep the existing implementation alongside the new and check if users have provided a custom Consumer factory and only use the new implementation when that isn't the case.

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