Set the container field of aconfig flags

Please see go/aconfig-flag-containers for more context

Test: m
Bug: 312769710
Change-Id: I51e76bd720981862a237d5e548887cd84dee92da
diff --git a/flags/telecom_calls_manager_flags.aconfig b/flags/telecom_calls_manager_flags.aconfig
index 1a19480..cdfcc30 100644
--- a/flags/telecom_calls_manager_flags.aconfig
+++ b/flags/telecom_calls_manager_flags.aconfig
@@ -1,4 +1,5 @@
 package: "com.android.server.telecom.flags"
+container: "system"
 
 flag {
   name: "use_improved_listener_order"