Added KILL QUERY command for MySQL client to cancel long-running queries

Why it matters

This feature addresses the need to terminate long-running queries initiated through MySQL-compatible clients or drivers, improving resource management and user control over query execution.

How to use it

Users can cancel a running query by executing the following command using a MySQL client or driver connected to ClickHouse:

KILL QUERY [connection_id];

where connection_id is the identifier of the session running the query to be killed.