[feat][broker][branch-3.0] PIP-321 Introduce allowed-cluster at the namespace level (#22378)

[Demogorgon314]

(cherry-picked from commit https://github.com/apache/pulsar/commit/36bae695fb07f3ee790bee603149c4c2712187e0)

Motivation

Cherry-picked from #22378

Modifications

Verifying this change

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

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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:

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• [ ] 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

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