Migrate ENABLE_TASKBAR_PINNING to aconfig flag

Test: Manual, Presubmit
Bug: 265437087
Flag: ACONFIG com.android.launcher3.enable_taskbar_pinning DISABLED

Change-Id: I4800230c04feceefa2398e189c493c8c4a7b2fe5
diff --git a/aconfig/launcher.aconfig b/aconfig/launcher.aconfig
index ace2210..fa76453 100644
--- a/aconfig/launcher.aconfig
+++ b/aconfig/launcher.aconfig
@@ -55,3 +55,10 @@
     description: "Enables launcher to listen to all transitions that include home activity"
     bug: "306053414"
 }
+
+flag {
+    name: "enable_taskbar_pinning"
+    namespace: "launcher"
+    description: "Enables taskbar pinning to allow user to switch between transient and persistent taskbar flavors."
+    bug: "270396583"
+}