Code changes per feedback:

1) Deprecate "collector.combiner.max-days-back" and replace with "collector.combiner.days-ago-to-start"
2) Rename new arg to match (1), collector.combiner.days-ago-to-end
3) Validate start > stop days.  Wonky due to lack of builtin cross field validation
4) Force secondary validation on StoredObjectCombiner per request