[improve][broker] Enhance logging for subscription creation failures due to NotAllowedException

[coderzc]

Motivation

2025-12-05T11:02:37,446+0000 [ForkJoinPool.commonPool-worker-2] ERROR org.apache.pulsar.broker.service.persistent.PersistentTopic - [persistent://pe/lab/result_pb-partition-1] Failed to create subscription: rw-consumer-855-7985
java.util.concurrent.CompletionException: org.apache.pulsar.broker.service.BrokerServiceException$NotAllowedException: Durable subscription with the same name already exists.

Modifications

Change log level form ERROR to Warn for NotAllowedException

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

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This change added tests and can be verified as follows:

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• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

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Matching PR in forked repository

PR in forked repository:

[github-actions]

@coderzc Please add the following content to your PR description and select a checkbox:

- [ ] `doc` <!-- Your PR contains doc changes -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
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[Technoboy-]

is it possible to add a test?