Enable Elderberry experiment in local finch config.

testing/variations/fieldtrial_testing_config.json

 {
     "AllBookmarks": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Disabled",
                     "disable_features": [
@@ skipping 1854 matching lines @@
             "experiments": [
                 {
                     "name": "Enabled"
                 },
                 {
                     "name": "Disabled"
                 }
             ]
         }
     ],
+    "TabManagementExperiment": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Elderberry"
+                }
+            ]
+        }
+    ],
     "TabSyncByRecency": [
         {
             "platforms": [
                 "android",
                 "chromeos",
                 "ios",
                 "linux",
                 "mac",
                 "win"
             ],
@@ skipping 312 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }