Reduce the number of write buffers for infrequently used column families

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/kvrocks/issues) and found no similar issues.

### Motivation

Currently, all column families are shared the same number of write buffers
which is unnecessary for infrequently used column families including `pubsub`,
`propagte`, and `zset_score`. We can keep them to a const value like 1 to reduce
the memory usage in some scenarios.

### Solution

_No response_

### Are you willing to submit a PR?

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