Full http logging

[andrewbaxter]

For http request issues (wrong headers, etc) a way to log full http requests and responses would be helpful.

I'd be happy to add this - should it be gated behind a config option somewhere?

[mcpherrinm]

I think this makes sense, and I also think it makes sense to have it configurable. While we're not using Go's "slog" library in Pebble so far, it might make sense to use it for this, and have the log level configurable. Then full HTTP logging can be behind a debug level log flag, disabled by default