Add container property.

Bug: 330354107
Test: CI

Change-Id: I508c4ef2db631b723f85269527367e0adc0fb14e
diff --git a/AconfigFlags.bp b/AconfigFlags.bp
index d98e191..c579870 100644
--- a/AconfigFlags.bp
+++ b/AconfigFlags.bp
@@ -585,6 +585,7 @@
 aconfig_declarations {
     name: "com.android.media.flags.performance-aconfig",
     package: "com.android.media.performance.flags",
+    container: "system",
     srcs: [
         "media/java/android/media/flags/performance.aconfig",
     ],