Google Cloud Logging doesn't show the correct level log when using
JsonFormatter, making observability a bit trickier. This applies minor
tweaks to the default format, allowing log entries to be properly
represented.
There are alternative packages to this but they add fields that aren't
strictly required - also performing `debug_backtrace()` calls that are
usually not desired when in production mode.
This is a backport of https://github.com/Seldaek/monolog/pull/1690
Signed-off-by: Luís Cobucci <lcobucci@gmail.com>
