[fix][admin] Avoid creating subscriptions when peeking messages if auto-creation is disabled

[void-ptr974]

Motivation

The peek messages Admin API implicitly creates a subscription at the earliest position when the requested subscription does not exist. This creation currently bypasses the effective allowAutoSubscriptionCreation policy at the topic, namespace, and broker levels.

As a result, a read-oriented Admin operation can create subscription metadata, retain backlog, and consume subscription quota even when automatic subscription creation is disabled.

Modifications

• Check the effective automatic subscription creation policy before implicitly creating a subscription for peek messages.
• Preserve the existing behavior of creating the subscription at the earliest position when automatic creation is allowed.
• Return HTTP 412 Precondition Failed when the subscription does not exist and automatic creation is disabled.
• Keep the subscription lookup and creation path asynchronous.
• Document the REST and Java Admin API behavior.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Extended PersistentTopicsTest.testPeekWithSubscriptionNameNotExist to verify that:
  • peeking does not create a subscription when automatic subscription creation is disabled;
  • the Java Admin client receives PreconditionFailedException;
  • peeking continues to create the subscription and return messages when automatic creation is enabled.
• Ran the relevant broker and client-admin-api Checkstyle tasks.
• Compiled the affected broker and client-admin-api modules.

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

• Dependencies (add or upgrade a dependency)
• The public API
  • peekMessages now reports PreconditionFailedException when the subscription is missing and automatic creation is disabled.
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
  • The peek message endpoint returns HTTP 412 for the rejected implicit subscription creation.
• The admin CLI options
• The metrics
• Anything that affects deployment