Support structured logging

[runofthemill]

Hello!

We run pint as a daemonset alongside our Prometheus statefulsets and while it's largely great & very helpful, GCP doesn't parse the logs at the right level since they're output to stderr and are just text logs:

Would you consider adding support for structured logging? I'd be happy to try a PR to add support via a flag, config file setting, or both. It looks like slog has a JSONHandler type, so I imagine it wouldn't be too difficult.

Cheers!