`clear-all.sh` should delete openmldb path if `OPENMLDB_USE_EXISTING_ZK_CLUSTER` is true

**Describe the feature you'd like**

`clear-all.sh` should delete zk path using `zk_client` if `OPENMLDB_USE_EXISTING_ZK_CLUSTER` is true. Now we only delete the zk data path if zk is deployed by us.

**Additional context**

Add any other context or screenshots about the feature request here.

Look at the clear-all.sh script to understand its current logic for deleting ZooKeeper data. Examine how OPENMLDB_USE_EXISTING_ZK_CLUSTER is used and where zk_client is invoked. The change involves adding a conditional branch to delete the zk path when using an existing ZooKeeper cluster. Check related scripts or documentation for the correct zk_client usage and path format.

Written by the indexing model from the issue text.