Addition of PeekTopic API to client library

[ijsong]

Background

The Varlog client library currently offers the PeekLogStream API to retrieve the first and last log sequence numbers in a log stream. However, since Varlog provides total ordering within a topic, not a log stream, users often need to find a topic's first and last log sequence numbers instead. At present, there is no direct method to fulfill this requirement.

Necessity

Improvement in user convenience: Given Varlog's characteristic of utilizing the total order of a topic, users frequently wish to know the start and end of a topic. The PeekTopic API can provide this information directly, enhancing the user experience.

Expected Impact

The PeekTopic API will enable users to quickly obtain a topic's first and last log sequence numbers. This will be particularly useful in large-scale data processing and real-time data streaming applications.
By expanding the range of APIs in the Varlog client library, a wider variety of use cases and requirements can be met.

Implementation Considerations

The PeekTopic API must efficiently query the metadata of a topic.
This API should maintain consistency with the existing PeekLogStream API while providing information specific to topics.