Add policy for /metadata/apex.

This is an area that apexd can use to store session metadata, which
won't be rolled back with filesystem checkpointing.

Bug: 126740531
Test: builds
Change-Id: I5abbc500dc1b92aa46830829be76e7a4381eef91
diff --git a/private/compat/27.0/27.0.ignore.cil b/private/compat/27.0/27.0.ignore.cil
index 1129259..fbd26a1 100644
--- a/private/compat/27.0/27.0.ignore.cil
+++ b/private/compat/27.0/27.0.ignore.cil
@@ -9,6 +9,7 @@
     adb_service
     app_binding_service
     apex_data_file
+    apex_metadata_file
     apex_mnt_dir
     apex_key_file
     apex_service