[Autofill Assistant] Add fieldtrial for Finch

Launch bug: crbug/1011334

Bug: none
Change-Id: I764fea997d4296b228826df49c8773bcb7675988
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2089778Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Sandro Maggi <sandromaggi@google.com>
Cr-Commit-Position: refs/heads/master@{#747903}

testing/variations/fieldtrial_testing_config.json

@@ -568,6 +568,22 @@
             ]
         }
     ],
+    "AutofillAssistantChromeEntryLaunch": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "//1": "This launch is gated external to Chrome.",
+                    "name": "Enabled",
+                    "enable_features": [
+                        "AutofillAssistantChromeEntry"
+                    ]
+                }
+            ]
+        }
+    ],
     "AutofillAssistantDirectActionsLaunch": [
         {
             "platforms": [