Allow reconfiguring log level on a per Fiber basis

Let's say in production you set the log level to `info`. Then a user reports a problem and you want to change the log level to `debug` *just* for you while you poke around.

I am not sure what the API looks like but I'd almost want to do something like

```crystal
if params.get?(:enable_super_special_log_just_for_me)
Log.current_fiber_level = :debug # Sets all logs to `:debug` *just* for the current Fiber
end
```

In a handler, before pipe, whatever. This would be super handy and I'd like to build something in for this at some point. So you can use Breeze in production but just with a special token set in the query param or a header

The issue names no files, tests, or entry points. Start by locating the logger configuration and how Fiber-local state is handled, then define an API for overriding the production log level only within the current Fiber. Done means a request can enable debug logging for itself without changing log levels for other Fibers.

Written by the indexing model from the issue text.