Add means to test whether debug logging is enabled

[keirlawson]

When attempting to port our application from Journal to log4cats 0.0.1 the first issue I encountered was there appears to be no way to test whether or not debug logging is enabled. We achieved this in Journal by using Logger.backend.isDebugEnabled.

[ChristopherDavenport]

So questioning, we want this as an attribute of the logger? I'm tempted to expose the underlying A within the algebra. However this is currently an artifactor of utilizing log4s so closely. It sounds like perhaps it would serve to build a core component with modules depending on the backends.

[keirlawson]

This strikes me as a fairly generic feature common to most loggers and fairly commonly used, so my preference would be to expose it as part of the log4cats logger without requiring a reference to the underlying implementation.