Make origin_visit_stats_get return results from all pages
psycopg2.extras.execute_values executes queries in batches of 100 by default. At the end of execute_values, only the last batch of results is available in the cursor; To fetch all results, one needs to set fetch=True instead of using the cursor.
Related to #3000 (closed) (and probably resolves it altogether).
Test Plan
added a unit test for proper behavior.
Migrated from D5068 (view on Phabricator)