Allow to delete keys by the prefix

### Search before asking

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

### Motivation

- Using Namespace in cluster mode to easily flush the keys .

### Solution

- As i knew namespace simply prepend the namespace prefix to the user key and remove it before retrieving. But it couldn't achieve with just simple key prefix.

we use the hash bracket like below, if our namespace is `foo`, and key is 1234, it will be successfully removed all the keys with same namespace.
{foo}:1234

### Are you willing to submit a PR?

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

Start by reviewing how namespaces and cluster-mode key deletion are handled, then trace the behavior of keys using the `{foo}:1234` hash-bracket prefix. The issue does not name files or tests, so first identify the relevant deletion entry point and existing coverage. Done means keys for a namespace can be deleted by prefix without removing unrelated keys.

Written by the indexing model from the issue text.