Fix fieldtrial_testing_config studies for Autofill local card migration flow

Create two studies since the two features have two different chrome
flags. Using one study would cause DCHECK failure (Feature has conflicting
field trial overrides) in Chromium debug mode.

Bug: 897998
Change-Id: Icf093329e30f660ce7697241f5fbcd0604a1f9ac
Reviewed-on: https://chromium-review.googlesource.com/c/1474277Reviewed-by: Jared Saul <jsaul@google.com>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Siyu An <siyua@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634846}

testing/variations/fieldtrial_testing_config.json

@@ -686,7 +686,7 @@
             ]
         }
     ],
-    "AutofillLocalCardMigrationWithFeedback": [
+    "AutofillLocalCardMigration": [
         {
             "platforms": [
                 "chromeos",
@@ -696,9 +696,26 @@
             ],
             "experiments": [
                 {
-                    "name": "EnableLocalCardMigrationWithFeedback",
+                    "name": "EnableLocalCardMigration",
+                    "enable_features": [
+                        "AutofillCreditCardLocalCardMigration"
+                    ]
+                }
+            ]
+        }
+    ],
+    "AutofillLocalCardMigrationShowFeedback": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "EnableLocalCardMigrationShowFeedback",
                     "enable_features": [
-                        "AutofillCreditCardLocalCardMigration",
                         "AutofillLocalCardMigrationShowFeedback"
                     ]
                 }