TaskManagerConfig set default zookeeper.cluster prop typo

**Bug Description**
`java/openmldb-taskmanager/src/main/java/com/_4paradigm/openmldb/taskmanager/config/TaskManagerConfig.java` line 303 set zookeeper.cluster prop typo
```java
if (props.getProperty("zookeeper.cluster") == null) {
props.setProperty("", "");
}
```

**Expected Behavior**
props.setProperty("zookeeper.cluster", "")

**Relation Case**

**Steps to Reproduce**

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The bug is in TaskManagerConfig.java line 303. Open the file, locate the if block that checks 'zookeeper.cluster', and replace the empty property set with the correct key and a default value. Run any existing tests for TaskManagerConfig to ensure the fix works.

Written by the indexing model from the issue text.