[ios][ScreenTime] Add testing config

Bug: 1133889
Change-Id: I671beba1defc45dfeebddc59ea5975202dcfa6d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2581337Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835292}

testing/variations/fieldtrial_testing_config.json

@@ -3683,6 +3683,21 @@
             ]
         }
     ],
+    "IOSScreenTimeIntegration": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ScreenTimeIntegration"
+                    ]
+                }
+            ]
+        }
+    ],
     "Identifiability": [
         {
             "platforms": [