Add flag for compose on keyguard.

Bug: 301968149
Test: NONE this just adds the flag. No change in behavior.
Flag: ACONFIG com.android.systemui.enable_keyguard_compose DEVELOPMENT

Change-Id: I32369dc652410ccfc8b647ef03cf4c50fc146391
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 7eca04a..f0e5048 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -371,3 +371,10 @@
    description: "Enables notification specific LinearLayout optimization"
    bug: "316110233"
 }
+
+flag {
+   name: "enable_keyguard_compose"
+   namespace: "systemui"
+   description: "Enables the compose version of keyguard."
+   bug: "301968149"
+}