Introduce Time-Bound Fallback ZooKeeper Sessions and Fix DNS Index Column

Why it matters

This feature enhances reliability by allowing ZooKeeper sessions to fallback temporarily within a specified time window, improving ZooKeeper connection handling. Additionally, it fixes the index column to correctly support DNS addresses in system tables, helping users better monitor ZooKeeper connections.

How to use it

Use the new time-bound fallback mechanism to improve ZooKeeper session stability with your existing ClickHouse configuration. Users will benefit from enhanced session handling automatically, and can verify ZooKeeper connections including DNS support via the fixed index column in system.zookeeper_connection.