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"
     ],
 }
 
diff --git a/aconfig/settings_onboarding_experience_flag_declarations.aconfig b/aconfig/settings_onboarding_experience_flag_declarations.aconfig
new file mode 100644
index 0000000..6fb5377
--- /dev/null
+++ b/aconfig/settings_onboarding_experience_flag_declarations.aconfig
@@ -0,0 +1,8 @@
+package: "com.android.settings.flags"
+
+flag {
+  name: "enable_sound_backup"
+  namespace: "onboarding_experience"
+  description: "Feature flag for B&R sound settings."
+  bug: "278975761"
+}