Switch from logrus to slog

[marstr]

I know that logrus isn't being as developed as actively as it once was, and I was just reading this article that was a pretty compelling case to switch to the newer API in the standard library, log/slog.

I don't think I ever really did a good job with tuning the logging behavior anyway. Right now a lot of noise gets piped to stderr and shown to the user when it doesn't really make sense.

My wish list would be to:

1. Add a global argument that controls the level of logging.
2. Add a global argument that controls where logs are written to.
3. Do a comprehensive review of what is logged here in baronial.
4. Adopt slog in https://github.com/marstr/envelopes as well so that debug information can be easily captured and shared here.