Add aConfig flag for battery level display.

Bug: 390542072
Flag: com.android.settings.flags.enable_battery_level_display
Test: N/A

Change-Id: Ifeb9a6122234e4d5712b4e583cd2de120d3e5149

aconfig/settings_bluetooth_declarations.aconfig

@@ -34,3 +34,13 @@ flag {
       purpose: PURPOSE_BUGFIX
   }
 }
+
+flag {
+  name: "enable_battery_level_display"
+  namespace: "cross_device_experiences"
+  description: "Show battery level when available"
+  bug: "380790573"
+  metadata {
+      purpose: PURPOSE_BUGFIX
+  }
+}