Hello!
We’re working on this.
We have a Github issue and at the moment we only add the pipeline.id on each log line IF the log is related to a specific pipeline.
We have another Pull Request (visible here) where we plan to have one log file per pipeline.
Both of those features are not released, but you can follow the development in those issues.
As this is a core Logstash feature, it will be necessary to update to new versions of Logstash.
Hope this will help you in the future!
Cheers,
Luca