Add aconfig flag: notification_content_alpha_optimization

Add aconfig flag: notification_content_alpha_optimization to control the fixing of HUN message flicker issue.

Bug: 292024656
Test: atest SystemUITests
Flag: ACONFIG notification_content_alpha_optimization DEVELOPMENT
Change-Id: I780273eb270be51356f1cb13d566ab6a994d51dc
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index a69a2a6..6f391f9 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -76,6 +76,16 @@
 }
 
 flag {
+    name: "notification_content_alpha_optimization"
+    namespace: "systemui"
+    description: "Only reset alpha values of needed content views"
+    bug: "292024656"
+    metadata {
+        purpose: PURPOSE_BUGFIX
+    }
+}
+
+flag {
     name: "notifications_live_data_store_refactor"
     namespace: "systemui"
     description: "Replaces NotifLiveDataStore with ActiveNotificationListRepository, and updates consumers. "