Add "enabled" configuration variable

[inakianduaga]

We need an "enabled" configuration variable that is true by default for both loggers. That way they can be dynamically disabled.

• Add a check for the flag in the code, if it's disabled it should do nothing, except return back the chain
• Update mock configuration/readme with examples
• Add tests for the disable case to make sure nothing is happening when disabled. Also add tests to dynamically toggle and make sure it works after reenabled.