Keeper improvement: support leadership_expiry_ms in settings

Why it matters

This feature enables better control over the leadership expiration timeout in ClickHouse Keeper, allowing users to customize the duration after which a leadership lease expires. It improves the stability and management of distributed coordination by reducing premature leadership changes or deadlocks.

How to use it

To use this feature, specify the leadership_expiry_ms parameter in the Keeper's settings configuration file or startup parameters with the desired expiration time in milliseconds.