MINOR: add helper function for clusterInstance

[TaiJuWu]

*More detailed description of your change, Add two helper function: clusterInstance#createTopic and cluster#consistentMetadata

Summary of testing strategy (including rationale) for the feature or bug fix. Unit and/or integration tests are expected for any behaviour change and system tests should be considered for larger changes.

Committer Checklist (excluded from commit message)

• [ ] Verify design and implementation
• [ ] Verify test coverage and CI build status
• [ ] Verify documentation (including upgrade notes)