core: add ids to gatherers

[connorjclark]

closes #2087

I suppose description would only be used when we print the status.

Do we especially want that, or do we just want an id instead of using the classname?

[patrickhulce]

I don't think this should live on the gatherer implementation. The grand unified view in the brain of me was that audits and gatherers have implementations that are id-agnostic, the config then creates an audit or gatherer instance by taking the implementation with a set of options and that instance has an id that can be referenced. This was the incarnation of audit/gatherer IDs that would've closed #2087 IMO --> #8374

If the id lives on the implementation then it doesn't really seem any different from using the class name like our audits basically do now.

[connorjclark]

alright, i've lost the thread here then. seems like that PR is what should land.