feat(specs): AB testing tracked user count (#2596)

Author: cdhawke

specs/abtesting/common/schemas/Variant.yml

@@ -72,8 +72,13 @@ variant:
       type: integer
       description: Number of users during the A/B test.
       example: 55501
+    trackedUserCount:
+      type: integer
+      description: Number of users that performed a tracked search during the A/B test.
+      example: 55501
   required:
     - userCount
+    - trackedUserCount
     - trafficPercentage
     - trackedSearchCount
     - searchCount