Add field trial testing config for password manager onboarding

Bug: 983445
Change-Id: I0c246798453ed8b940ae65cd9ac32739a0b001d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1798354Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Andrei Chulkov <achulkov@google.com>
Cr-Commit-Position: refs/heads/master@{#695987}

testing/variations/fieldtrial_testing_config.json

@@ -468,6 +468,21 @@
             ]
         }
     ],
+    "AndroidPasswordManagerOnboarding": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "PasswordManagerOnboardingAndroid"
+                    ]
+                }
+            ]
+        }
+    ],
     "AndroidSpellChecker": [
         {
             "platforms": [