Add event_time_microseconds to system.asynchronous_metric_log and system.metric_log tables

Why it matters

This feature enhances the granularity of metric logging by storing event timestamps with microsecond precision. It allows users to perform more precise monitoring and analysis of asynchronous and synchronous metrics within ClickHouse.

How to use it

Users can query the event_time_microseconds column directly from the system.metric_log and system.asynchronous_metric_log tables to access event timestamps at microsecond resolution.