Enable system server to read pm.archiving.enabled system property, as system server will need this check to have the archiving feature during testing.

Change-Id: Ia75f3ea0570075e9600548e24e42f17a783187ba
Bug: 321730881
Test: Presubmit
diff --git a/private/system_server.te b/private/system_server.te
index 6ba7d4a..f4d2aaa 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -1576,3 +1576,7 @@
   -dumpstate
   -system_server
 } threadnetwork_config_prop:file no_rw_file_perms;
+
+# Allow system server to read pm.archiving.enabled prop
+# TODO(azilio): Remove system property after archiving testing is completed.
+get_prop(system_server, pm_archiving_enabled_prop)