Add flag for B&R sound settings

Bug: 278975761
Test: adb shell device_config put onboarding_experience com.android.settings.flags.enable_sound_backup true
Change-Id: Ia774b1d5f3740b4964eb3cb1501ea4779f203956
diff --git a/aconfig/Android.bp b/aconfig/Android.bp
index d4960c2..d0a8afe 100644
--- a/aconfig/Android.bp
+++ b/aconfig/Android.bp
@@ -9,6 +9,7 @@
         "settings_connecteddevice_flag_declarations.aconfig",
         "settings_globalintl_flag_declarations.aconfig",
         "settings_apn_flag_declarations.aconfig",
+        "settings_onboarding_experience_flag_declarations.aconfig"
     ],
 }