Add possibility to configure logging level for production duct configuration

[lucassousaf]

The idea is to add the :level key to the logging config of the production profile and set it as an environment variable. Like:

duct.logger/timbre
{...
:level #duct/env ["LOG_LEVEL" Keyword]
...
}

[lucassousaf]

If we want a more fine grained configuration Timbre (our underlying logging implementation) accepts a lot more configuration: http://ptaoussanis.github.io/timbre/taoensso.timbre.html#var-*config* and http://ptaoussanis.github.io/timbre/taoensso.timbre.html#var-default-config