Add example for changing logging level of a single logger

[Guillemdb]

We want to add a tutorial exaplining how to set the log level of specific loggers within our codebase.

@vmarkovtsev I forgot how to set environment variables to target specific loggers. For example if my logger name is lib.module I would like to run my app so that the logging level defaults to INFO for all loggers except this one, that should be DEBUG.

I remember it was something like

LOG_LEVEL=INFO "lib.module.log_level=DEBUG" python my_script.py

Do you remember how it was done? I would like to add an example to the docs so I don't forget again.