[Autofill] Field trial config for the Frecency experiment.

testing/variations/fieldtrial_testing_config_ios.json

 {
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillProfileOrderByFrecency": [
         {
             "group_name": "EnabledLimitTo3",
             "params": {
                 "limit": "3"
             }
+        },
+        {
+            "group_name": "Enabled"
         }
     ],
     "ChromotingQUIC": [
         {
             "group_name": "Enabled"
         }
     ],
     "DataCompressionProxyDevRollout": [
         {
             "group_name": "Control"
@@ skipping 48 matching lines @@
     ],
     "VarationsServiceControl": [
         {
             "group_name": "Interval_30min",
             "params": {
                 "fetch_period_min": "30"
             }
         }
     ]
 }