[DS][x/n] Allow SchedulingConditions to target specific dependency keys

[OwenKephart]

Summary & Motivation

This is a long-standing request. It's often useful to be able to detect the status of some specific set of dependency keys, rather than needing to treat all dependencies identically.

This creates a single structure for defining and resolving these sorts of collections, but does not export it as a top-level user-facing concept, as that feels a bit like jumping the gun.

This allows users to explicitly select any keys they want to select for, as well as explicitly ignore some specific keys, as either workflow is potentially useful. An explicit choice was made to not error when an "invalid" selection (i.e. one that references keys that are not dependencies) is made, as this would be pretty annoying (imo).

How I Tested These Changes