Apply loglevels in the environment

[helje5]

When switching to the "official" Logging package, we lost the ability to easily set loglevels? Like export LOGLEVEL=trace.

We should fix that and have Macro configure the logging system if such env vars are found.

Boilerplate:

LoggingSystem.bootstrap { label in
  var handler = StreamLogHandler.standardOutput(label: label)
  handler.logLevel = .trace
  return handler
}