[filebeat] optimise adding file owner and group to the events' meta fields

[AndersonQ]

#47878 introduced adding file owner and group to the events' meta fields. However it adds 2 syscalls to the hot path and a micro-benchmark shows it might have a non-negligible impact on the overall performance.

This issue is to optimise it, remove the syscalls from the hot path. It might be enough to get the file owner and group once per file, cache it, and use the cached values when populating the event's meta fields

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)