Add a modifiable factory for SLF4J loggers

[freya022]

I think it would be nice if we could set our own way to get a org.slf4j.Logger from the name, for example this could allow returning a fallback logger, when no logging implementation is detected, in this example I could use this method.

I assume this could be implemented by having a mutable property in KotlingLogging, which would get used by KLoggerFactory.logger.

This would also avoid checking the kotlin-logging-to-jul property for every logger, by checking once and using the right factory.

Caveats

This is modifiable by anyone, it could get overwritten by accident by an end user of a library that did set that property

Workarounds

Use your own function to get a KLogger

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[oshai]

I think maybe a better approach is to implement the fallback logger you linked in this lib. I saw many cases that logging was misconfigured in slf4j, and their approach of not logging info messages in that case is something we can consider to change.

Ref: https://stackoverflow.com/questions/56270497/how-to-get-slf4j-console-output-when-no-implementation-is-present