add namespace get-topic-auto-creation cmd

[nlu90]

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Motivation

pulsarctl namespaces had set-topic-auto-creation and remove-topic-auto-creation, but it was missing get-topic-auto-creation. That made it impossible to check the namespace-level setting directly from the CLI.

Modifications

Added get-topic-auto-creation to the namespace commands and wired it to the existing admin API.

Verifying this change

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

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

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

Documentation

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[github-actions]

@nlu90:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[nlu90]

Test:

== Create namespace ==

+ ./bin/pulsarctl -s http://localhost:8080 namespaces create public/test-topic-auto-creation-1773422021
Created public/test-topic-auto-creation-1773422021 successfully

== Set topic auto-creation ==
Set topic auto-creation config successfully for [public/test-topic-auto-creation-1773422021]

== Get topic auto-creation ==
{
  "allowAutoTopicCreation": true,
  "topicType": "partitioned",
  "defaultNumPartitions": 2
}

== Remove topic auto-creation override ==
Removed topic auto-creation config successfully for [public/test-topic-auto-creation-1773422021]

== Verify override removed ==
null