Add ITradeInMode service sepolicy.

This defines a new service for the ITradeInMode, and grants it (through
system_server) permissions to modify persist.adb.tradeinmode.

Bug: 307713521
Test: manual test
Change-Id: I0afb349863aaf8488dd3dabaf8e7319e297bffaf
diff --git a/private/service.te b/private/service.te
index 1f31477..69f1b77 100644
--- a/private/service.te
+++ b/private/service.te
@@ -33,6 +33,7 @@
     type supervision_service, app_api_service, ephemeral_app_api_service, system_server_service, service_manager_type;
 ')
 type tracingproxy_service,          system_server_service, service_manager_type;
+type tradeinmode_service,           system_server_service, service_manager_type;
 type transparency_service,          system_server_service, service_manager_type;
 
 is_flag_enabled(RELEASE_AVF_ENABLE_DEVICE_ASSIGNMENT, `