Fix the namespace for aconfig flag

- Reference b/290822399
- The namespace of aconfig flag should be "power_optimization", not
  "battery_saver"

Test: Manual Test
Bug: 336960905
Change-Id: I8e4e272a4a792eef2d624fabe1938f23b0c8b292
diff --git a/services/core/java/com/android/server/power/batterysaver/flags.aconfig b/services/core/java/com/android/server/power/batterysaver/flags.aconfig
index fa29dc1..059c4a4 100644
--- a/services/core/java/com/android/server/power/batterysaver/flags.aconfig
+++ b/services/core/java/com/android/server/power/batterysaver/flags.aconfig
@@ -3,7 +3,7 @@
 
 flag {
   name: "update_auto_turn_on_notification_string_and_action"
-  namespace: "battery_saver"
+  namespace: "power_optimization"
   description: "Improve the string and hightligh settings item for battery saver auto-turn-on notification"
   bug: "336960905"
   metadata {