Reset partitions of a topic

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Motivation

There is a API for increase partitions for a topic https://pulsar.apache.org/admin-rest-api/?version=3.3.0#operation/PersistentTopics_updatePartitionedTopic
but it only accept a greater number (as the doc says, it should be **incremental**).

I'm wondering if it's possible to decrease a existing partitioned topic, otherwise, I have to copy my topic to a new one and delete it manually.

### Solution

_No response_

### Alternatives

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [X] I'm willing to submit a PR!

Start with the admin REST API's updatePartitionedTopic operation linked in the issue and inspect how it enforces increasing the partition count. Determine the constraints and design implications of decreasing partitions; done requires a maintainer-approved approach for the API behavior and its documentation or implementation scope.

Written by the indexing model from the issue text.