Add aconfig feature flag for multi instance menu in Taskbar

Test: Presubmit
Fix: 355237285
Flag: com.android.launcher3.enable_multi_instance_menu_taskbar
Change-Id: I049ebe3808223a9d7e96251c8cdb3134d9a9be28
diff --git a/aconfig/launcher.aconfig b/aconfig/launcher.aconfig
index 21b9863..b3253d1 100644
--- a/aconfig/launcher.aconfig
+++ b/aconfig/launcher.aconfig
@@ -316,3 +316,10 @@
     description: "Archived apps will use new icon in app title"
     bug: "350758155"
 }
+
+flag {
+    name: "enable_multi_instance_menu_taskbar"
+    namespace: "launcher"
+    description: "Menu in Taskbar with options to launch and manage multiple instances of the same app"
+    bug: "355237285"
+}
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