Custom format log

[bizy01]

want to support custom format logging

[mingrammer]

Still in needs?

[crolfe]

I'm not sure if this is what the original requestor is looking for, but something that would be useful to me is the ability to define some sort of schema for json format logs. I am using flog to generate logs for testing a log processing pipeline, and it would be nice to be able to define my own fields and have control over the name of the keys and type/range/format of the associated values, so I can test my pipeline with realistic data.