Write A/B test for AND operator relaxation test described in T114773.
The primary idea here is to integrate with the existing TestSearchSatisfaction schema. Split the users into two buckets with half as control, and half participating in the test. There is a special query parameter which enables the common terms query, this should be set for all search queries (top-right search bar when enter is pressed, along with Special:Search) that are participating the test and not in the control bucket.
The schema needs to additionally record which bucket (control or test) the user is in.