Add changes to bring up Keystore Certificate post processor.

Adds a system property which denotes the presence of a post processor.
Also adds the policies for the post processor service that is needed for
the processor to work correctly.

Test: manual check with test cert processor.
Bug: 361877215
Change-Id: I5feb0a250e2856189d5b4165187dcb415790e529
diff --git a/private/file_contexts b/private/file_contexts
index fa2fe3a..e26fb4e 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -362,7 +362,8 @@
 /system/bin/virtual_camera          u:object_r:virtual_camera_exec:s0
 /system/bin/hw/android\.frameworks\.bufferhub@1\.0-service    u:object_r:fwk_bufferhub_exec:s0
 /system/bin/hw/android\.system\.suspend-service               u:object_r:system_suspend_exec:s0
-/system/etc/aconfig(/.*)?                u:object_r:system_aconfig_storage_file:s0
+/system/bin/rkp_cert_processor          u:object_r:rkp_cert_processor_exec:s0
+/system/etc/aconfig(/.*)?               u:object_r:system_aconfig_storage_file:s0
 /system/etc/cgroups\.json               u:object_r:cgroup_desc_file:s0
 /system/etc/task_profiles/cgroups_[0-9]+\.json               u:object_r:cgroup_desc_api_file:s0
 /system/etc/event-log-tags              u:object_r:system_event_log_tags_file:s0