Add SettingsAddPaymentMethod to the field trial config

Bug: none
Change-Id: I60a3cdad143ac8e414415c1d03c34e59e843e34b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864779
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707046}

testing/variations/fieldtrial_testing_config.json

@@ -3000,6 +3000,21 @@
             ]
         }
     ],
+    "IOSSettingsAddPaymentMethod": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "SettingsAddPaymentMethod"
+                    ]
+                }
+            ]
+        }
+    ],
     "ImprovedRecoveryComponent": [
         {
             "platforms": [