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_contexts b/private/service_contexts
index 37652ae..8e537b9 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -466,6 +466,7 @@
 thermalservice                            u:object_r:thermal_service:s0
 thread_network                            u:object_r:threadnetwork_service:s0
 tracing.proxy                             u:object_r:tracingproxy_service:s0
+tradeinmode                               u:object_r:tradeinmode_service:s0
 translation                               u:object_r:translation_service:s0
 transparency                              u:object_r:transparency_service:s0
 trust                                     u:object_r:trust_service:s0