Display extra fields (non req/res)

[rohit-gohri]

Currently the printer only prints specific fields from req/res and timestamps. If we added extra fields through something like the customReqProps feature in pino-http (pinojs/pino-http#103) they will not be printed.

This could be added by default or behind an option (not sure what the name could be, --extra?)

[mcollina]

Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[rohit-gohri]

Yes, will do. I'll try to get it done this week.