Change namespace of flag to 'onboarding'

Test: atest -v SystemBackupAgentTest
Bug: 296844513
Change-Id: Ia7aed9b33115612a0733956551615ae6d775999c
diff --git a/services/backup/flags.aconfig b/services/backup/flags.aconfig
index 4022e33..1416c88 100644
--- a/services/backup/flags.aconfig
+++ b/services/backup/flags.aconfig
@@ -11,7 +11,7 @@
 
 flag {
     name: "enable_metrics_system_backup_agents"
-    namespace: "backup"
+    namespace: "onboarding"
     description: "Enable SystemBackupAgent to collect B&R agent metrics by passing an instance of "
             "the logger to each BackupHelper."
     bug: "296844513"