[WIP] - Cache Reaper

Created by: goddardcm

Fixes #627.

Adds a creaper cmd that can be used to monitor and reduce cache directory size. I've annotated the PR inline.

Not sure what approach we'd like to take for getting this binary running within any of the existing docker containers. Likely we would need to create wrapper start scripts that would invoke both the main binary as well as starting creaper in the background.

Also worth noting that this implementation isn't testable. I wavered a bit on how much effort to put toward making it testable and decided against it at least for the first pass. If we did want some test coverage for the code, i'd advocate for concentrating those efforts on the clearSpace function (given a slice of cachedFile and other parameters, ensure that the expected files would be deleted) and not really worrying about testing the getDirectoryInfo function)