Currently when using $graphLookup there is no easy way to make the evaluation stop as soon as certain criteria is met. For example, if I want to find the shortest path from A to B, I can't use $graphLookup efficiently, since it wouldn't stop evaluation as soon as B is found. It continues until no more matching documents are found, or until the operation reaches a recursion depth specified by the maxDepth parameter.

Maybe we we add some field like `limit : <integer>` this can be solved. For the above case user can specify `limit: 1` so that we can stop evaluation as soon as we find the first object.