Flush topic contents Request

# What is currently missing?

Ability to flush contents of a topic through Klaw. As a developer, it is required sometimes to flush the contents, and it can only be done by Kafka Admins, by resetting the retention period.

# How could this be improved?

Create a new request type for this at topic level.

# Is this a feature you would work on yourself?

* [ ] I plan to open a pull request for this feature