Add query_start_time_microseconds field to system.query_log and system.query_thread_log tables

Why it matters

This feature enhances the precision of query start time tracking in ClickHouse system logs, enabling more detailed performance analysis and troubleshooting by capturing the exact start time down to microseconds.

How to use it

Users can access the new query_start_time_microseconds field directly in queries against the system.query_log and system.query_thread_log tables. No additional configuration is required; the field is available by default after upgrading to the version containing this feature.