Implement filtering on dataset actions

We already have broad actions working:

Dataset:
  potentialAction:
    - name: "exclude"

Now we want to add patterns, so that this action can be applied to a specific subset of files in the directory:

Dataset:
  potentialAction:
    - name: "exclude"
      pattern: ".*\\.png"

Short term, we should support regex patterns, but in future we may also want to incorporate glob style patterns (e.g. "*.png")