Add flag for customizing touchpad 3 finger tap.

Test: Manual. Adding flag.
Flag: com.android.systemui.touchpad_three_finger_tap_customization
Bug: 376249366
Change-Id: I73bf605d315d939f451a6aca09bd417e3f9b6b01
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 5c5edb1..b0bd5b7 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -1708,3 +1708,9 @@
     bug: "365064144"
 }
 
+flag {
+   name: "touchpad_three_finger_tap_customization"
+   namespace: "systemui"
+   description: "Customize touchpad three finger tap"
+   bug: "365063048"
+}