Introduce an ITradeInMode service.

This is used by the DeviceDiagnostics app to enter trade-in mode during setup wizard.

Bug: 307713521
Test: manual test
Flag: com.android.tradeinmode.flags.enable_trade_in_mode
Change-Id: Ib1b4b2979a17aa63ab5e45701ed038e348348f9a
diff --git a/AconfigFlags.bp b/AconfigFlags.bp
index deb6f13..55e6239 100644
--- a/AconfigFlags.bp
+++ b/AconfigFlags.bp
@@ -21,6 +21,7 @@
     java_aconfig_libraries: [
         // !!! KEEP THIS LIST ALPHABETICAL !!!
         "aconfig_mediacodec_flags_java_lib",
+        "aconfig_trade_in_mode_flags_java_lib",
         "android-sdk-flags-java",
         "android.adaptiveauth.flags-aconfig-java",
         "android.app.appfunctions.flags-aconfig-java",