Add fieldtrial config for SyncTriggerFullKeystoreMigration

Bug: 1094326
Change-Id: Iba070069d1dfc82f450defccf2eebf4d9b46480c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2390908
Commit-Queue: Maksim Moskvitin <mmoskvitin@google.com>
Auto-Submit: Maksim Moskvitin <mmoskvitin@google.com>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805243}

testing/variations/fieldtrial_testing_config.json

@@ -6587,6 +6587,26 @@
             ]
         }
     ],
+    "SyncTriggerFullKeystoreMigration": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "SyncTriggerFullKeystoreMigration"
+                    ]
+                }
+            ]
+        }
+    ],
     "SynchronousPageFlipTesting": [
         {
             "platforms": [