[php-slim4] Add monolog package as default logger

Created by: ybelenko

I've added pre-configured Monolog logger. Big projects might need logger factory to use different logger instances in each micro service, but current implementation should cover MVP.

This code enables logger with production mode only, it's based on my personal job experience because I don't read log files during development. From my point of view enabled logger at the dev server just pollutes system with temp files which I won't read anyway, in rare cases when I do need logs(CRON task) I turn them on manually.

@wing328 if you know how to change folder permissions from the Java code let me know. It would be great to make logs folder writable(like from command line sudo chmod a+w logs)

cc @jebentier @dkarlovi @mandrean @jfastnacht @renepardon

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