Add the testharness service to sepolicy rules

The testharness service will manage Test Harness Mode and provide a
command-line interface for users to enable Test Harness Mode; however it
does not directly provide a public API.

Bug: 80137798
Test: make
Test: flash crosshatch
Change-Id: Ie396e40fcea8914b4dd2247f2314e029b66ad84e
diff --git a/private/service_contexts b/private/service_contexts
index 5448183..2ad99eb 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -181,6 +181,7 @@
 task                                      u:object_r:task_service:s0
 telecom                                   u:object_r:telecom_service:s0
 telephony.registry                        u:object_r:registry_service:s0
+testharness                               u:object_r:testharness_service:s0
 textclassification                        u:object_r:textclassification_service:s0
 textservices                              u:object_r:textservices_service:s0
 time_detector                             u:object_r:timedetector_service:s0