feat(abtests): update estimate response type

Author: cdhawke

specs/abtesting/common/schemas/EstimateABTestResponse.yml

@@ -6,13 +6,13 @@ EstimateABTestResponse:
       format: int64
       description: Estimated number of days needed to reach the sample sizes required for detecting the configured effect. This value is based on historical traffic.
       example: 21
-    controlSampleSize:
-      type: integer
-      format: int64
-      description: Number of tracked searches needed to be able to detect the configured effect for the control variant.
-      example: 23415
-    experimentSampleSize:
-      type: integer
-      format: int64
-      description: Number of tracked searches needed to be able to detect the configured effect for the experiment variant.
-      example: 23415
+    sampleSizes:
+      type: array
+      description: |
+        Sample size estimates for each variant. The first element is the control variant.
+        Each element is the estimated number of searches required to achieve the desired statistical significance.
+      items:
+        type: integer
+        format: int64
+        description: Number of tracked searches needed to be able to detect the configured effect for the control variant.
+        example: 23415