feat(data-modeling): allow partial documents match when discovering relationships on ObjectId fields

[gribnoysup]

Based on this scope discussion, trying out relationships inference with some of the sample data sets, and a recent discussion with product, we want to make the inference algorithm slightly more forgiving for one specific case: when _id field is of type ObjectId, we can be pretty confident that we're looking at a real relationship if even a single matching document is found, so instead of looking for an exact match with sample documents count, we will look for at least one matching doc.