Add Async Metrics for Virtual Memory Mappings VMMaxMapCount and VMNumMaps

Why it matters

These metrics provide enhanced visibility into the virtual memory mappings of the ClickHouse server. By tracking VMMaxMapCount and VMNumMaps, users can better understand and manage system resource usage, helping to identify potential memory mapping issues and optimize performance.

How to use it

The new metrics VMMaxMapCount and VMNumMaps are available asynchronously within the ClickHouse metrics system. Users can query these metrics using existing monitoring tools integrated with ClickHouse's metrics endpoint or system tables without additional configuration.