Allow < and > to work with lists

[edahlseng]

It would be super helpful if the < and > (and <=/>=) operators worked with lists, whereby listA < listB means that every element in listA is in listB. This makes it possible to make rules like the following:

conditions:
  - commented-reviews-by<=approved-reviews-by

This is needed for the above example because GitHub does not clear the commented review state for a user when they approve a PR (instead it just adds an approving review in addition to the commented review).

If desired I can try to help with this issue, but would need a pointer as to where this logic is located!