Add container to .aconfig

Change-Id: I404c5ad928d22d82ffae613d7efe84993dfdc9af
Test: m
Bug: 328444881
diff --git a/libs/WindowManager/Shell/aconfig/multitasking.aconfig b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
index b61dda4..7ff204c 100644
--- a/libs/WindowManager/Shell/aconfig/multitasking.aconfig
+++ b/libs/WindowManager/Shell/aconfig/multitasking.aconfig
@@ -1,4 +1,5 @@
 package: "com.android.wm.shell"
+container: "system"
 
 flag {
     name: "enable_app_pairs"