Add apexd_payload_metadata_prop

This should be read-only and corresponds to apexd.payload_metadata.path

Bug: 191097666
Test: android-sh -c 'setprop apexd.payload_metadata.path'
See permission denied
atest MicrodroidHostTestCases

Change-Id: Ifcb7da1266769895974d4fef86139bad5891a4ec
diff --git a/private/property.te b/private/property.te
index b196a1b..7033a06 100644
--- a/private/property.te
+++ b/private/property.te
@@ -1,5 +1,6 @@
 # Properties used only in /system
 system_internal_prop(adbd_prop)
+system_internal_prop(apexd_payload_metadata_prop)
 system_internal_prop(ctl_snapuserd_prop)
 system_internal_prop(device_config_lmkd_native_prop)
 system_internal_prop(device_config_profcollect_native_boot_prop)
@@ -376,6 +377,15 @@
 }:property_service set;
 
 neverallow {
+  # Only allow init to set apexd_payload_metadata_prop
+  domain
+  -init
+} {
+  apexd_payload_metadata_prop
+}:property_service set;
+
+
+neverallow {
   # Only allow init and shell to set userspace_reboot_test_prop
   domain
   -init