[ISSUE #786] Return unavailable for consumer group providers

[Aias00]

Which Issue(s) This PR Fixes

Fixes #786

Brief Description

The default Consumer Group metadata/admin implementations now return explicit BusinessException(501, ...) responses when the backing provider is not configured, instead of throwing plain UnsupportedOperationException and surfacing as generic 500 errors.

This keeps the current Topic paths untouched and only changes Consumer Group operations used by /api/groups.

How Did You Test This Change?

• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn -Dtest=CloudMetadataProviderTest,NameSrvAdminClientTest,MetadataServiceTest test
• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn -Dtest=ConsumerGroupControllerTest test

[Copilot]

Pull request overview

This PR hardens the default Consumer Group provider/admin stubs so /api/groups operations fail with an explicit BusinessException(501, ...) (“not configured”) instead of UnsupportedOperationException, allowing the global exception handler to return HTTP 501 rather than a generic 500.

Changes:

• Update CloudMetadataProvider Consumer Group query methods to throw BusinessException(501, ...) when no provider is configured.
• Update NameSrvAdminClient Consumer Group admin methods to throw BusinessException(501, ...) when no admin client is configured.
• Add focused unit tests verifying the new 501 behavior and message for both default implementations.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
server/src/main/java/org/apache/rocketmq/studio/instance/topic/NameSrvAdminClient.java	Switch Consumer Group admin operations from UnsupportedOperationException to BusinessException(501, ...) for clearer API behavior.
server/src/main/java/org/apache/rocketmq/studio/instance/topic/CloudMetadataProvider.java	Switch Consumer Group metadata operations from UnsupportedOperationException to BusinessException(501, ...) for clearer API behavior.
server/src/test/java/org/apache/rocketmq/studio/instance/topic/NameSrvAdminClientTest.java	Add assertions that default admin client returns BusinessException with code 501 + expected message for Consumer Group operations.
server/src/test/java/org/apache/rocketmq/studio/instance/topic/CloudMetadataProviderTest.java	Add assertions that default metadata provider returns BusinessException with code 501 + expected message for Consumer Group operations.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.