Add sepolicy for AppIntegrityService.

CL that adds the service: http://ag/9554748

BUG:145674997
Test: Manually flash the device. Without this change, the devices goes into a
bootloop (http://gpaste/5033431010377728) if I uncommit the guard in
http://ag/c/platform/frameworks/base/+/9652133/21/services/core/java/com/android/server/integrity/AppIntegrityManagerService.java

Change-Id: Ib2daf9191900d94abeae207e18a77a5914d14783
diff --git a/private/service_contexts b/private/service_contexts
index 1902a48..09afd65 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -10,6 +10,7 @@
 android.security.keystore                 u:object_r:keystore_service:s0
 android.service.gatekeeper.IGateKeeperService    u:object_r:gatekeeper_service:s0
 app_binding                               u:object_r:app_binding_service:s0
+app_integrity                             u:object_r:app_integrity_service:s0
 app_prediction                            u:object_r:app_prediction_service:s0
 app_search                                u:object_r:app_search_service:s0
 apexservice                               u:object_r:apex_service:s0