Allow a logger instance to be injected via the configuration

[schleyfox]

Currently, config can specify the options to be passed to the constructed winston logger, but the specific transport is hard coded as Console. Some applications may wish to use other transports like Syslog that are defined in other packages.

This change adds a config field, loggerInstance, that allows an arbitrarily constructed logger to be passed in. Really any object that implements log should work, but this is intended for other winston loggers.

/cc @goatslacker

[schleyfox]

@goatslacker PTAL

[goatslacker]

Can you please rebase?